1
UNIVERSITA’ DEGLI STUDI DI PARMA
DOTTORATO DI RICERCA IN
SCIENZE DELLA TERRA
CICLO XXXIV
MANTLE HETEROGENEITIES IN RIFTING-RELATED
AND SUPRA-SUBDUCTION SETTINGS: EXAMPLES
FROM EXTERNAL LIGURIAN AND NEW CALEDONIA
OPHIOLITES
Coo dina o e:
Chia .mo P o . Ma co Ro e i
Tu o e:
Chia .ma P o .ssa Alessand a Mon anini
Co-Tu o e:
Chia .mo P o . Ricca do T ibuzio
Do o ando: Elisa Fe a i
Anni Accademici 2018/2019 – 2020/2021
2
3
Index
Chap e 1 6
1.1. In oduc ion: con en s and aims o he Thesis 6
1.2. Re e ences 7
Chap e 2-Ri ing e olu ion o he li hosphe ic subcon inen al man le: New insigh s
om he Ex e nal Ligu ian ophioli es (No he n Apennine, I aly) 8
2.1. In oduc ion 8
2.2. Geological se ing 9
2.3. Field ela ionships 12
2.3.1. Mon e Ga i man le sec ion 12
2.3.2. Mon e San ’Agos ino man le sec ion 13
2.4. Pe og aphic cha ac e is ics and majo elemen mine al chemis y 15
2.4.1. Mon e Ga i pe ido i es 15
2.4.2. Mon e Ga i Type-I py oxeni es 15
2.4.3. Mon e Ga i Type-II py oxeni es 16
2.4.4. Mon e San ’Agos ino de o med pe ido i es 17
2.4.5. Mon e San ’Agos ino spinel-plagioclase webs e i es 18
2.5. Geo he moba ome ic es ima es 24
2.5.1. Mon e Ga i man le sec ion 24
2.5.2. Mon e San ’Agos ino man le sec ion 25
2.6. Discussion 25
2.6.1. Mon e Ga i: a man le sec ion eco ding eac i e mel in il a ion in he
plagioclase s abili y ield 25
2.6.2. Mon e San 'Agos ino: a de o med man le sec ion 27
2.6.3. The di e se na u e o py oxeni es om he Ex e nal Ligu ian man le 31
sec ions
2.6.4. The he e ogenei y o he Ex e nal Ligu ian subcon inen al man le 33
2.6.5. Cons ain s on he man le e olu ion in he Wes e n Te hys 35
ocean-con inen ansi ion
2.7. Conclusions 39
2.8. Re e ences 40
4
2.9. Tables 48
Chap e 3-Insigh s on he Mon e Ga i plagioclase- acies mel - ock eac ion e en 56
3.1. In oduc ion 56
3.2. Geological and pe ological amewo k 57
3.3. Me hodology 58
3.4. Whole ock composi ions 59
3.5. Mine al ace elemen composi ions 63
3.6. Geo he mome ic es ima es 64
3.7. Nd-H iso opic composi ions 70
3.8. Discussion 73
3.8.1. Geochemical esponse o plagioclase- acies mel in il a ion 73
3.8.2. The mal e olu ion o he Mon e Ga i sequence 74
3.8.3. Iso opic cons ain s on he mel in il a ion e en 75
3.8.3.1. The Uppe T iassic mel imp egna ion e en 76
3.9. Conclusions 77
3.10. Re e ences 79
3.11. Tables 84
Chap e 4-Ouassé (New Caledonia) py oxeni es wi ness man le he e ogenei y in
young subduc ion sys ems 92
4.1. In oduc ion 92
4.2. Geological and pe ological se ing 92
4.3. Field ela ionships and sampling 96
4.4. Me hodology 97
4.5. Pe og aphy and mine alogy 100
4.5.1. Ha zbu gi es 100
4.5.2. O hopy oxeni es 101
4.5.3. Amphibole-bea ing webs e i es 101
4.6. Whole ock composi ions 108
4.6.1. Majo elemen s 108
4.6.2. T ace elemen s 108
4.7. Mine al ace elemen s composi ion 109
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4.7.1. O hopy oxeni es 109
4.7.2. Amphibole-bea ing webs e i es 113
4.8. Geo he mome y 117
4.9. 40A /39A amphibole da ing 118
4.10. Discussion 118
4.10.1. Na u e and e olu ion o hos ing pe ido i es 118
4.10.2. O igin o he py oxeni e laye s 120
4.10.2.1. O hopy oxeni es 120
4.10.2.2. Amphibole-bea ing webs e i es 122
4.10.3. Insigh s on he New Caledonia Paleocene-Eocene subduc ion ini ia ion 124
4.10.4. E olu ion o he pe cola ing mel s/ luids in he o ea c man le 127
4.10.5. Hin s o ein e p e ing he signi icance o he Bogo a Peninsula
Shea Zone 128
4.11. Conclusions 129
4.12. Re e ences 129
4.13. Tables 138
Chap e 5 149
5.1. Concluding ema ks 149

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Chap e 1
1.1. In oduc ion: con en s and aims o he Thesis
The no ion o man le he e ogenei y has become en enched in he scien i ic communi y since he
pionee ing s udies in he 1960s, which e idenced geochemical and iso opic a iabili ies in he oceanic
basal s, one o he main p oduc s o man le mel ing (Hedge and Wal hall, 1963; Gas e al., 1964;
Ta sumo o e al., 1965; Schilling and Winches e , 1967, 1969; Gas , 1968; Ha , 1971). S udying
Mid-Ocean Ridge Basal s (MORB) and Ocean Island Basal s (OIB) has always been a widely used
me hod o cha ac e ize man le sou ces, al hough i is an indi ec in es iga ion app oach. A di ec
app oach is ep esen ed by sampling man le ocks om he ocean loo , by d edging o d illing, and
ophioli ic exposu es, besides analysing man le xenoli hs.
Man le he e ogenei ies a e gene ally explained by he p esence o py oxeni e and eclogi e laye s,
which, o a la ge ex en , could de i e om p ocesses o c us al ecycling in o he man le (i.e.,
subduc ion and li hosphe ic delamina ion). The guiding heme o his PhD Thesis is he c ea ion o
geochemical and iso opic he e ogenei ies in man le sequences om dis inc geodynamic se ings, in
pa icula om i ing- ela ed and young sup a-subduc ion se ings. Speci ic pe ogene ic p ocesses
ac in hese di e en en i onmen s: while li hosphe ic ex ension and as henosphe e upwelling
domina e he i ing- ela ed se ing, p oduc ion o mel s om a iably deple ed man le sou ces
modi ied by slab-de i ed componen s a e belie ed o cha ac e ize he subduc ion onse .
Two dis inc ophioli ic exposu es a e conside ed in he p esen s udy: he Ex e nal Ligu ian
ophioli es, chosen as an example o i ing- ela ed man le sec ion and he New Caledonia ophioli e,
chosen as an example o sup a-subduc ion zone man le sec ion.
Chap e 2 and Chap e 3 illus a e he Ex e nal Ligu ian case s udy. In pa icula , he main
objec i es o Chap e 2 a e: (i) o desc ibe he pe og aphic, pe ological and geochemical
cha ac e is ics o wo poo ly known man le bodies (Mon e Ga i and Mon e San ’Agos ino), and (ii)
o p o ide new insigh s in o he beha iou o he Ex e nal Ligu ian subcon inen al man le du ing he
Mesozoic i ing phase. The con en s o Chap e 2 ep esen a pape al eady published: Fe a i E.,
Mon anini A., T ibuzio R., 2022. Ri ing e olu ion o he li hosphe ic subcon inen al man le: New
insigh s om he Ex e nal Ligu ian ophioli es (No he n Apennine, I aly). Li hos, 410-411: 106571.
The a icle is epo ed unchanged in he Thesis, excep o he layou . Chap e 3 ocuses on: (i) he
mel - ock eac ion p ocess eco ded by Mon e Ga i man le body, and (ii) he o igin o he
imp egna ing mel .
7
Chap e 4 illus a es he New Caledonia case s udy. The main pu pose is o de ine he
composi ions o he mel s pe cola ing he o ea c man le du ing he subduc ion ini ia ion.
1.2. Re e ences
Gas P.W., 1968. T ace elemen ac iona ion and he o igin o holeii ic and alkaline magma ypes.
Geochimica e Cosmochimica Ac a, 32:1057-1086
Gas P.W., Til on G.R., Hedge C., 1964. Iso opic composi ion o lead and s on ium om Ascension
and Gough Islands. Science, 145:1181-1185
Ha S.R., 1971. K, Rb, Cs, S , Ba con en s and S iso ope a ios o ocean loo basal s. Philosophical
T ansac ions o he Royal Socie y Se ies A, 268:573-587
Hedge C.E., Wal hall F.G., 1963. Radiogenic s on ium 87 as an index o geological p ocesses.
Science, 140:1214-1217
Schilling J.G., Winches e J.W., 1967. Ra e-ea h ac iona ion and magma ic p ocesses. Man les o
Ea h and Te es ial Plane s, 267-283, Runcon SK, London: In e science Publishe s
Schilling J.G., Winches e J.W., 1969. Ra e ea h con ibu ion o he o igin o Hawaiian la as.
Con ibu ions o Mine alogy and Pe ology, 40:231
Ta sumo o M., Hedge C.E., Engel A.E.J., 1965. Po assium, ubidium, s on ium, ho ium, u anium,
and he a io o s on ium-87 o s on ium-86 in oceanic holeii ic basal . Science, 150:886-888
8
Chap e 2
Ri ing e olu ion o he li hosphe ic
subcon inen al man le: New insigh s
om he Ex e nal Ligu ian ophioli es
(No he n Apennine, I aly)
2.1. In oduc ion
Magma-poo ocean-con inen ansi ions (OCT), such as hose exposed along he Ibe ia-
New oundland (e.g., Whi ma sh e al., 2001) and he Aus alian-An a c ic sys ems (e.g., McCa hy
e al., 2020), a e cha ac e ized by wide a eas o subcon inen al man le upli ed and denuded in
conjunc ion wi h he la e-s age i ing e olu ion. A key poin o elucida e he i ing p ocess leading
o basin opening is he e o e he ec onic, magma ic and me amo phic e olu ion o he subcon inen al
li hosphe ic man le. In pa icula , limi ed di ec in o ma ion a e a ailable on he high empe a u e
shea ing and mode o man le exhuma ion be o e he la e coupling s age, whe e b i le aul s cu
h ough he ex emely hinned con inen al c us and pene a e in o he unde lying man le (Su a and
Mana schal, 2012). Samples d illed o d edged along mode n OCTs es i y he occu ence o
he e ogeneous subcon inen al li hosphe ic man le, which p ese es geochemical signa u es acqui ed
be o e onse o i ing, as well as e idence o syn- i mel - ock in e ac ion and de o ma ion (e.g.,
Chazo e al., 2005; Mün ene and Mana schal, 2006). Howe e , he ela i ely limi ed sampling
compa ed wi h he egional ex en o he in ol ed a eas, and he di use al e a ion o he eco e ed
samples hampe ed o en isage a concep ual model o he man le beha iou om he beginning o
li hosphe ic hinning o c us al b eakup.
F agmen s o magma-poo ocean-con inen ansi ions o Ju assic age a e exposed along he
Alpine-Apennine bel (e.g., Mana schal and Mün ene , 2009). These ossil eco ds p o ided ele an
in o ma ion abou he i ing- ela ed his o y unde gone by he subcon inen al man le du ing
li hosphe e hinning and exhuma ion (e.g., Picazo e al., 2016). Fo ins ance, he in es iga ion o he
Pla a ophioli es om Cen al Alps documen ed ha he subcon inen al man le was pe cola ed and
e e ilized by MORB- ype mel s du ing i ing (e.g., Mün ene e al., 2010). In addi ion, he cen al
body o he Lanzo man le massi om Wes e n Alps p o ides e idence o mel ocusing wi hin
i ing- ela ed plagioclase- acies shea zones (Kaczma ek and Mün ene , 2010; Kaczma ek and
9
Tommasi, 2011). The subcon inen al man le bodies om he Ex e nal Ligu ian uni s (No he n
Apennines, Fig. 1) a e also pa o a Ju assic magma-poo ocean-con inen ansi ion (Ma oni e al.,
1998). Despi e some o hese man le bodies we e ho oughly in es iga ed om pe ological,
geochemical and mic os uc u al iewpoin s (e.g., Bo ghini e al., 2016; Hidas e al., 2020; Mon anini
e al., 2006; Rampone e al., 1995), a comp ehensi e i ing- ela ed geological scena io is lacking o
he Ex e nal Ligu ian man le sec ion.
The p ima y aim o his con ibu ion is o p o ide new cons ain s on he e olu ion o he
subcon inen al man le in ol ed in a i ing p ocess. We hus p esen new ield, mic os uc u al,
mine al chemis y and geo he moba ome ic da a ob ained o pe ido i es and enclosed py oxeni es
om kilome e-sized subcon inen al man le bodies om he Ex e nal Ligu ian uni s, locally
ecognized as Mon e Ga i and Mon e San 'Agos ino. To ou knowledge, no pe og aphic and
pe ological da a a e a ailable in he li e a u e o hese man le sec ions. We documen ha he
di e en man le bodies om he Ex e nal Ligu ian uni s display dis inc ec onic and he mal
e olu ions in he plagioclase s abili y ield. Hence, we ela e he he e ogeneous beha iou o he
subcon inen al man le unde ela i ely low p essu e condi ions o he i ing p ocess ha ul ima ely
de eloped a magma-poo Ju assic OCT. A compa ison wi h ophioli ic man le sec ions om he
Alpine bel inally allowed us o shed ligh on he i ing- ela ed e olu ion o he subcon inen al
li hosphe ic man le a a egional scale.
2.2. Geological se ing
The ophioli ic bodies exposed along he Alpine-Apennine bel a e li hosphe ic emnan s o he
Wes e n Te hys (o Ligu ian-Piedmon ese basin). This basin o med in he Middle o Uppe Ju assic
in conjunc ion wi h he opening o he Cen al A lan ic Ocean and sepa a ed he Eu ope-Ibe ia om
he A ica-Ad ia pla e (e.g. Sche ino and Tu co, 2011). The opening o Wes e n Te hys basin was
associa ed wi h upli and denuda ion o subcon inen al li hosphe ic man le, which is p esen ly
exposed along he Alpine-Apennine bel . Du ing i ing and oceaniza ion, he subcon inen al
li hosphe ic man le mos likely unde wen he mochemical e osion d i en by eac ion wi h ascending
mel s o as henosphe ic o igin (e.g., Mün ene e al., 2010; Picca do e al., 2004, 2007; Rampone e
al., 2020).
The Alpine-Apennine ophioli es a e locally associa ed wi h con inen al c us ma e ial and
equen ly include man le sec ions e aining a subcon inen al o igin (e.g., Mana schal and Mün ene ,
2009; Ma oni e al., 1998). The bes examples o p ese ed subcon inen al man le we e epo ed o
he Malenco-To alp bodies om Cen al Alps (Mün ene e al., 2004, 2010) and o he Ex e nal
Ligu ian uni s om he No he n Apennine (e.g., Mon anini e al., 2006, 2012; Rampone e al., 1995).
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homogeneous TiO2 (0.7–0.9 w %). The coa se g een spinels (C # = 2–4, TiO2 < 0.10 w %) a e
immed by 1–2 mm hick plagioclase co onas (Fig. 2.5c). The selec ed sample also includes smalle ,
submillime e o millime e-scale spinel g ains wi h da k b own colou and embayed shape, immed
by up o 1 cm wide agg ega es made up o al e ed plagioclase and mino oli ine (Fig. 2.4a). These
spinels ha e a iable and signi ican ly highe C # (12–34) and TiO2 (0.15–1.02 w %). No ably, mino
amoun s o ela i ely la ge chlo i e g ains displaying p isma ic shape and ghos clea ages,
p esumably ep esen ing pseudomo phs a e o hopy oxene, a e also p esen . Hence, we en ision
ha he o iginal mine al assemblage o hese py oxeni es was mos ly composed o clinopy oxene,
associa ed wi h mino amoun s o Al-spinel and o hopy oxene.
Type-Ib py oxeni es (samples GA1 and MG6) a e cha ac e ized by he occu ence o dis inc
py oxene- and plagioclase-bea ing domains, which a e bo h up o 2 cm long (Fig. 2.3d). The
py oxene- ich domains a e composed o clinopy oxene (40–50 ol%), o hopy oxene (35–40 ol%)
and mino plagioclase (15–20 ol%), and locally include elics o p e-exis ing coa se clinopy oxenes
(Fig. 2.5d). Thick plagioclase + o hopy oxene lamellae a e p esen along he clea ages o hese
coa se clinopy oxenes, ypically o ming symplec i ic in e g ow hs (Fig. 2.5e). The coa se
clinopy oxene has ela i ely low Mg# (79–84) and a iable Al2O3 (5.2–9.7 w %), TiO2 (1.2–2.3 w %)
and Na2O (0.4–1.7 w %), wi h no clea sys ema ic zoning (Fig. 2.8). The chemical composi ions o
he seconda y clinopy oxenes associa ed wi h plagioclase and o hopy oxene all wi hin hese
in e als. O hopy oxene has low Mg# (81–83), 1.9–3.7 w % Al2O3, 0.6–1.3 w % CaO and ela i ely
high TiO2 (0.3–0.5 w %). Accesso y b own amphibole ( i anian pa gasi e acco ding o he
nomencla u e o Leake e al., 1997) occu s as hin ims man ling eso bed clinopy oxenes and has
76–80 Mg# and 2.7–3.8 w % TiO2. The plagioclase- ich domains include ~30 ol% oli ine and, in
hei inne po ions, accesso y amoun s o small spinel g ains wi h b ownish-black colou (Fig. 2.5 ).
Plagioclase (71–79 mol% ano hi e) and oli ine (82–83 mol% o s e i e) o m nea ly polygonal
agg ega es and a e a iably al e ed in o se ici e and se pen ine, espec i ely. Spinel wi hin he
plagioclase- ich domain has a iable C # (4–30) and TiO2 (0.10–0.56 w %, Fig. 2.7). Tiny ilmeni e
and al e ed Fe-Ni-Cu sul ides wi h ounded mo phology a e also in places p esen wi hin plagioclase.
Towa ds he con ac wi h he py oxene- ich domains, coa se-g ained e micula oli ine + plagioclase
in e g ow hs ypically occu .
2.4.3. Mon e Ga i Type-II py oxeni es
Type-II py oxeni es a e medium- o coa se-g ained oli ine webs e i es. They display mode a e o
ex ensi e se pen iniza ion, which makes in places di icul o deciphe hei p ima y ex u e.
Howe e , in he mos p ese ed samples, an allo iomo phic g anula ex u e is disce nible. Thei

17
o iginal mine al assemblage is composed o clinopy oxene (30–40 ol%), o hopy oxene (25–30
ol%), oli ine (up o 25 ol%), g eenish o b own spinel (5–10 ol%) and plagioclase (10–15 ol %).
These py oxeni es a e cha ac e ized by he p esence o exsol ed o hopy oxene po phy oclas s,
o s e i e- ich (89 mol%) oli ine (Fig. 2.5g) ha is locally kinked, and clinopy oxene- ich domains.
These domains consis o i egula ly shaped clinopy oxene g ains wi h plagioclase + o hopy oxene
lamellae (Fig. 2.5h), associa ed wi h in e s i ial plagioclase and ails o elonga ed spinels immed by
plagioclase.
Clinopy oxene om Type-II py oxeni es has 88–90 Mg#, ela i ely high C 2O3 (0.4–0.9 w %)
and a wide TiO2 ange (0.7–1.8 w %; Figs. 2.8 and 2.9). Al2O3 and Na2O in clinopy oxene a y om
4.5 o 7.4 w % and om 0.5 o 0.9 w %, espec i ely. O hopy oxene displays high Mg# (87–89),
4.0–5.8 w % Al2O3 and 0.6–1.0 w % CaO. Spinel has a iable C # (6–16) and 0.1–0.6 w % TiO2
(Fig. 2.7). Plagioclase is in mos places eplaced by se ici e, bu small p ese ed domains wi h ~65
mol% ano hi e we e ound in sample IC2/3. Accesso y b own amphibole ( i anian pa gasi e) occu s
as im a ound py oxenes and is cha ac e ized by 85–87 Mg# and 3.1–4.0 w % TiO2.
2.4.4. Mon e San ’Agos ino de o med pe ido i es
The Mon e San 'Agos ino pe ido i es mos ly consis o plagioclase- acies myloni ic lhe zoli es
including small (cm- o dm-sized) domains made up o spinel- acies ec oni es. Mic os uc u al
e idence o a spinel- acies ec ys alliza ion e en a e p ese ed in hese low-s ain domains (Fig.
2.10a), whe e up o 1 cm in size po phy oclas s o clinopy oxene and o hopy oxene a e su ounded
by ine-g ained g anoblas ic agg ega es made up o py oxenes + ligh b own spinel ± o ange-b own
amphibole. Mu ual exsolu ions a e displayed by he o hopy oxene and he clinopy oxene
po phy oclas s (Fig. 2.10a-b), and he o e all clinopy oxene mode a ies be ween 10 and 15 ol%.
In he less se pen inized samples, mm-sized oli ine po phy oclas s su ounded by neoblas ic oli ine
a e s ill ecognizable. Holly lea b own spinels a e also locally p ese ed.
The spinel- acies assemblage is widely o e p in ed by a plagioclase- acies myloni ic ab ic. The
myloni e mic os uc u e is cha ac e ized by po phy oclas s o o hopy oxene and clinopy oxene
aligned along he olia ion (Fig. 2.10b–c). C -spinel and a e b own amphibole may also occu as
po phy oclas s. Po phy oclas ic o hopy oxene ypically displays up o ~10 aspec a io (Fig. 2.10c).
Po phy oclas ic clinopy oxene is smalle and mo e equan han associa ed po phy oclas ic
o hopy oxene. Bo h py oxene po phy oclas s p o ide e idence o de o ma ion, like undulose
ex inc ion, bending and kinking, and a e se in o a polyphase oli ine- ich ma ix wi h ex emely ine
g ain-size (20–50 μm, Fig. 2.10b-c-d). Besides oli ine, his ma ix includes neoblas ic clinopy oxene
and o hopy oxene, plagioclase and, in places, C -spinel. Plagioclase also occu s as hin ims man ling
18
he spinel po phy oclas s. The ex emely ine-g ained ma ix is dominan in he ul amyloni es (Fig.
2.10e), which con ain spo adic py oxene and b own amphibole po phy oclas s wi h ounded shape
(Table 2.3).
Bo h po phy oclas ic and ma ix oli ine ha e 89–90 mol% o s e i e and 0.4–0.5 w % NiO.
Po phy oclas ic clinopy oxene has 90–91 Mg# and high Al2O3 and Na2O con en s (7.0–8.4 w % and
1.6–2.1 w %, espec i ely), sligh ly dec easing om he co e o he im (Fig. 6). Clinopy oxene
neoblas s ha e highe Mg# alues (91–92) and lowe Al2O3 and Na2O (2.3–3.2 and ~0.6 w %,
espec i ely) han po phy oclas s (see also Fig. 2.6). O hopy oxene po phy oclas s ha e 89–90 Mg#,
4.4–5.6 w % Al2O3 and 0.7–0.9 w % CaO. The iny o hopy oxene om he myloni ic ma ix is
dis inc in he low Al2O3 (0.5–2.4 w %) and CaO (0.25–0.36 w %). Spinel has low C # (9–16) and
TiO2 ≤ 0.20 w % (Fig. 2.7). Plagioclase in he myloni ic ma ix has 38–50 mol% ano hi e.
Po phy oclas ic amphibole is i anian pa gasi e, wi h 84–86 Mg# and 3.1–4.6 w % TiO2. Accesso y
amphibole wi h ela i ely low TiO2 (~1.8 w %, Table 2.3) is also p esen in he ma ix o he
ul amyloni es.
2.4.5. Mon e San ’Agos ino spinel-plagioclase webs e i es
These py oxeni es ypically ha e p o omyloni ic ex u e (Fig. 2.10 -g). Po phy oclas s o
exsol ed clinopy oxene and o hopy oxene (up o 0.5 cm in size), and o Al-spinel a e se in o a ine-
g ained neoblas ic ma ix displaying an a e age g ain size o ~0.1 mm (Fig. 2.10 -g). Compa able
amoun s o clinopy oxene and o hopy oxene po phy oclas s a e gene ally obse ed. The
clinopy oxene po phy oclas s (Fig. 2.10g) locally display hin exsolu ion lamellae o o hopy oxene
± plagioclase, and he o hopy oxene po phy oclas s a e equen ly s e ched along he main olia ion.
The neoblas ic mine al assemblage consis s o clinopy oxene and o hopy oxene associa ed wi h
mino o accesso y amoun s o g een spinel, plagioclase, oli ine and b own amphibole. The
neoblas ic mine als commonly display g ain bounda y alignmen pa allel o he myloni ic olia ion.
Webs e i e MP7 also includes ounded symplec i ic domains (Fig. 2.10h) made up o e micula C -
poo spinel (C # ~1), Al-poo o hopy oxene (Al2O3 = 2.8–3.9 w %) and mino plagioclase (52–54
mol% ano hi e).
Taken as a whole, clinopy oxenes and o hopy oxenes ha e 84–88 Mg# and 83–88 Mg#,
espec i ely (Table 2.4). Clinopy oxene po phy oclas co es ha e high amoun s o Al2O3 (9–10 w %)
and, acco dingly, high p opo ions o Ca-Tsche mak subs i u ion (up o ~15 mol%), which a e
coupled wi h 0.8–1.1 w % Na2O (Fig. 8). O hopy oxene is also Al2O3- ich (4.9–6.8 w %), wi h a he
uni o m CaO (0.5–0.7 w %). Fo bo h py oxenes, a dec ease o Al2O3 is obse ed in po phy oclas
ims and in neoblas ic g ains wi h espec o po phy oclas ic co es. G een spinel has gene ally low
19
C # (< 0.15 w % TiO2, Fig. 2.7). Oli ine and plagioclase in he myloni ic ma ix ha e 80–88 mol%
o s e i e and 54–55 mol% ano hi e. B own amphibole is i anian pa gasi e o kae su i e wi h 79–83
Mg# and 3.2–5.4 w % TiO2.
Fig. 2.4. Thin sec ion (4.6 mm × 2.6 mm) images o :
(a) Type-Ia py oxeni e (sample GAV2), (b)
p o omyloni ic lhe zoli e (sample IC12–3), (c)
myloni ic lhe zoli e (sample MGO1).
20
Fig. 2.5. Thin sec ion pho omic og aphs unde c oss-pola ized (a-b-d-e- -g-h) and plane-pola ized
ligh (c) o Mon e Ga i samples. (a) embayed clinopy oxene pa ially eplaced by o hopy oxene +
(al e ed) plagioclase, pe ido i e MGA7; (b) o hopy oxene + (se ici ized) plagioclase eplacing
clinopy oxene, Type-Ia py oxeni e GAV2; (c) Al-spinel immed by plagioclase, Type-Ia py oxeni e
GAV2; (d) py oxene- ich domain, Type-Ib py oxeni e MG6; (e) symplec i ic o hopy oxene-
plagioclase in e g ow h in clinopy oxene, Type-Ib py oxeni e MG6; ( ) plagioclase- ich domain,
Type-Ib py oxeni e GA1; (g) Mg- ich oli ine, Type-II py oxeni e IC2–3; (h) O hopy oxene and
plagioclase coa se lamellae in clinopy oxene, Type-II py oxeni e IC2–3.
21
Fig. 2.6. Va ia ion o Na2O s.
Al2O3 o clinopy oxenes om Mon e
Ga i and Mon e
San 'Agos ino pe ido i es;
p c = po phy oclas , neo = neoblas .
Da a sou ces o o he Ex e nal
Ligu ian pe ido i es: Bo ghini e al.,
2011, Bo ghini e al.,
2013; Mon anini e al.
(2006); Rampone e al. (1995). No h
Lanzo da a om Kaczma ek e al.
(2008); Uppe Pla a, Malenco and
To alp da a om Mün ene e al.
(2010).
Fig. 2.7. Va ia ion o C #
(100 ⋅[C /(C + Al)]) s.
TiO2 o spinel om Mon e
Ga i and Mon e
San 'Agos ino pe ido i es and
py oxeni es. Da a sou ces o
o he Ex e nal Ligu ian
pe ido i es and py oxeni es:
Bo ghini e al. (2011, 2013,
2016); Mon anini e al.
(2006); Rampone e al.
(1995). Da a o No h Lanzo
pe ido i es om Kaczma ek
and Mün ene (2008); Uppe
Pla a, Lowe Pla a,
Malenco and To alp
pe ido i es a e Mün ene e
al. (2010). Da a o Mon e
Maggio e py oxeni es
(Co sica) om Basch e al.
(2019).

22
Fig. 2.8. Va ia ion o Na2O and
TiO2 s. Al2O3 o clinopy oxenes
om Mon e Ga i and Mon e
San 'Agos ino py oxeni es; p c =
po phy oclas , neo = neoblas , 1 =
cpx in p ima y ga ne -bea ing
assemblage, 2 = cpx in e og ade,
ga ne - ee assemblage. Da a
sou ces o o he Ex e nal Ligu ian
py oxeni es: Bo ghini e al. (2016),
Mon anini e al. (2006). Da a o
Mon e Maggio e py oxeni es
(Co sica) om Basch e al. (2019).
Fig. 2.9. Va ia ion o C 2O3 s. Mg#
(100 ⋅[Mg/(Mg + Fe o )]) o
clinopy oxenes om Mon e Ga i and
Mon e San 'Agos ino pe ido i es and
py oxeni es; p c = po phy oclas .
23
Fig. 2.10. Thin sec ion pho omic og aphs unde c oss-pola ized ligh (a-b-c-e- -g), plane-pola ized ligh
(h) and BSE (back-sca e ed elec on) image (d) o Mon e San 'Agos ino samples. (a) P ese ed
po phy oclas ic domain in pe ido i e wi h de o med o hopy oxene man led by ine-g ained neoblas ic
agg ega es o o hopy oxene + clinopy oxene + spinel (p o omyloni e IC12–3); (b-c) Exsol ed clino- and
o hopy oxene po phy oclas s in polyphase plagioclase-bea ing myloni ic ma ix (lhe zoli e IC8–1); (d)
BSE image o polyphase plagioclase-bea ing myloni ic ma ix (lhe zoli e sample IC 8–3); (e) pe ido i e
ul amyloni e wi h ounded py oxene po phy oclas s cu by se pen ine eins (sample IC11); ( )
O hopy oxene po phy oclas s in webs e i e wi h p o omyloni ic ex u e (sample AM489); (g) Exsol ed
clinopy oxene po phy oclas in webs e i e wi h p o omyloni ic ex u e (sample MP7); (h) Symplec i ic
o hopy oxene-spinel-plagioclase domain a e ga ne (sample MP7).
24
2.5. Geo he moba ome ic es ima es
Tempe a u e e alua ions o he di e en equilib a ion s ages eco ded by he Mon e Ga i and
Mon e San 'Agos ino pe ido i es and enclosed py oxeni e laye s we e ob ained using con en ional
py oxene geo he mome y (Table 2.5). In pa icula , he wo-py oxene geo he mome e (B ey and
Kohle , 1990 and Taylo , 1998, e e ed o as TBK90 and TTa98, espec i ely) and Ca-in-o hopy oxene
geo he mome e (B ey and Kohle , 1990, e e ed o as TCa-in-Opx) we e applied. Fo he Mon e Ga i
Type-I py oxeni es and he Mon e San 'Agos ino webs e i es, we also calcula ed he equilib a ion
empe a u es (THB94) based on he amphibole-plagioclase me hod o Holland and Blundy (1994).
A aluable ool applicable o he plagioclase-bea ing pe ido i es o he p esen s udy is he
geoba ome e o Fumagalli e al. (2017), which elies on he p essu e-sensi i e equilib ium Fo s e i e
+ Ano hi e = Ca-Tsche mak + Ens a i e (FACE) and has a s anda d e o o 0.05 GPa. No ably, he
applica ion o he FACE geoba ome e o py oxeni es has been ecen ly e alua ed by Basch e al.
(2020), who ob ained sligh ly highe p essu e es ima es o webs e i es han o enclosing pe ido i es.
In pa icula , a sys ema ic p essu e di e ence o ~0.1 GPa was ela ed o he lowe C # o he
webs e i es compa ed wi h he pe ido i es, which led o highe Ca-Tsche mak ac i i y in he
webs e i e clinopy oxene. Conside ing he unce ain ies epo ed by Basch e al. (2020), we applied
he FACE geoba ome e o no only he pe ido i es bu also he enclosed py oxeni es (Table 2.5).
2.5.1. Mon e Ga i man le sec ion
Tempe a u e es ima es o Mon e Ga i samples we e calcula ed o :
(i) La ge o hopy oxene-clinopy oxene g ains om pe ido i e MGA7 and Type-II
py oxeni e IC2/3. The co es o exsol ed o hopy oxene po phy oclas s yielded TCa-in-
Opx o 950–1110 °C, assuming a con ining p essu e o 1.5 GPa. Tempe a u e es ima es
ob ained om wo-py oxene geo he mome y o he pe ido i e MGA7 a e shi ed o
lowe alues (897–938 °C).
(ii) Non-exsol ed o hopy oxenes o med in conjunc ion wi h plagioclase in Type-I and
Type-II py oxeni es. The ob ained empe a u es (TCa-in-Opx) all in a wide ange (910–
1065 °C), ega dless o di e en ex u al occu ences o o hopy oxene. The
empe a u es in e als ob ained om adjacen clinopy oxene-o hopy oxene pai s
(TTa98 = 845–983 °C, TBK90 = 876–1015 °C) a e sligh ly lowe han TCa-in-Opx.
Howe e , he a e age TCa-in-Opx (974 ± 47 °C) a e wi hin e o o he a e age TTa98 (913
± 52 °C) and TBK90 (937 ± 47 °C).
25
(iii) Coexis ing amphibole and plagioclase in Type-I py oxeni e GA1, which ga e
empe a u e es ima es o 1030 °C using he me hod o Holland and Blundy (1994).
P essu e es ima es by FACE geoba ome e (Fumagalli e al., 2017) we e only compu ed o he
Mon e Ga i py oxeni es, as he enclosing pe ido i es lack p ese ed plagioclase. We used he same
clinopy oxene-o hopy oxene pai s employed o wo-py oxene geo he mome ic calcula ions and
ob ained p essu e alues anging om 0.67 o 0.78 GPa.
2.5.2 Mon e San ’Agos ino man le sec ion
Exsol ed po phy oclas co es om myloni ic lhe zoli es ga e ela i ely low clinopy oxene-
o hopy oxene (TTa98 = 832–886 °C, TBK90 = 857–950 °C) and Ca-in-Opx empe a u e es ima es
(930–970 °C). Tempe a u e e alua ions alling in he same in e als o sligh ly shi ed owa ds highe
alues we e ob ained o he webs e i e po phy oclas ic assemblage (TTa98 = 914–958 °C, TBK90 =
940–960 °C and TCa-in-Opx = 919–985 °C).
The ex emely ine-g ained py oxenes om he ma ix o myloni ic and ul amyloni ic lhe zoli es
yielded TTa98 and TBK90 o 756–873 °C and TCa-in-Opx o 750–780 °C. In addi ion, an amphibole-
plagioclase pai om ul amyloni ic lhe zoli e IC11 ga e a alue o 778 °C based on he Holland and
Blundy (1994) me hod. In he webs e i es, we ob ained: (i) TTa98 = 856–880 °C, TBK90 = 905–938 °C
and TCa-in-Opx = 870–930 °C om he neoblas ic py oxenes associa ed wi h plagioclase, and (ii) 880–
907 °C based on he plagioclase-amphibole me hod by Holland and Blundy (1994).
Applica ion o he FACE geoba ome e (Fumagalli e al., 2017) indica e shallow condi ions o
he de elopmen o plagioclase-bea ing assemblage in he myloni ic lhe zoli es. P essu e alues o
0.54–0.55 GPa and 0.34 GPa we e ob ained om lhe zoli es IC8–1 and IC8–3 and IC11, espec i ely.
The webs e i es ga e p essu e s ima es o 0.77–0.90 GPa.
2.6. Discussion
2.6.1. Mon e Ga i: a man le sec ion eco ding eac i e mel in il a ion in he
plagioclase s abili y ield
The Mon e Ga i ha zbu gi e-py oxeni e associa ion is nea ly unde o med and cha ac e ized by
ex ensi e c ys alliza ion o plagioclase ± o hopy oxene a he expense o spinel and clinopy oxene.
In bo h he ha zbu gi es and he enclosed py oxeni es, plagioclase no only occu s as co onas a ound
spinel bu also wi hin la ge clinopy oxene g ains as pa ches o hick lamellae associa ed wi h
o hopy oxene (Fig. 2.5a-b-h), locally o ming symplec i ic in e g ow hs (Fig. 2.5e). An exsolu ion
o igin o his plagioclase-o hopy oxene associa ion is unlikely, gi en he high p opo ions o hese
32
bodies (Mon anini e al., 2006). The Mon e San 'Agos ino webs e i es also ha e highly aluminous
clinopy oxene po phy oclas s wi h plagioclase + o hopy oxene exsolu ions, simila o hose de i ed
om e og ession o p ima y Na-Al- ich clinopy oxene o iginally in equilib ium wi h ga ne . In
addi ion, bo h he Mon e San 'Agos ino and he Rio S ega-Mon e P inze a webs e i es (see also
Mon anini and T ibuzio, 2015) a e cha ac e ized by simila wo-py oxene equilib a ion empe a u es
ob ained o he po phy oclas ic spinel- acies assemblage (i.e., TBK90 o 940–960 °C and 900–980 °C,
espec i ely), and p o omyloni ic ex u es de eloped in he plagioclase s abili y ield.
The Mon e Ga i py oxeni es do no display high empe a u e de o ma ion mic os uc u es and
p o ide e idence o pe asi e mel in il a ion unde plagioclase- acies condi ions, con a y o wha
was obse ed o he o he Ex e nal Ligu ian man le bodies. On he o he hand, he p esence o
py oxeni es wi h dis inc hickness and Mg#, as sugges ed by he clinopy oxene chemis y (79–87
and 88–90 in Type-I and Type-II py oxeni es, espec i ely; Fig. 2.9), was also ecognized o he Rio
S ega-Mon e P inze a lhe zoli e-py oxeni e sec ion (Mon anini e al., 2006). The p ima y modal
composi ion o Type-I ( hick, Fe- ich) py oxeni es is di icul o es ablish, due o he ex ensi e
ans o ma ions ela ed o he p ocess o mel - ock eac ion. We specula e ha he Type-I py oxeni e
p o oli hs we e coa se-g ained spinel- ich o hopy oxene-poo webs e i es. In addi ion, he low Mg#
o clinopy oxene sugges s c ys alliza ion in a mel -domina ed sys em, wi h a negligible mass
con ibu ion om enclosing lhe zoli es. Type-II ( hin, Mg- ich) py oxeni es we e spinel-bea ing
oli ine webs e i es. The p esence o de o med o s e i e- ich oli ine and Mg- ich exsol ed
o hopy oxene in Type-II py oxeni es, simila o hose occu ing in he hos pe ido i es, documen s
o ma ion by mel /pe ido i e hyb idiza ion, p esumably h ough a p ocess leading o oli ine
consump ion and concomi an c ys alliza ion o Mg- ich clinopy oxene + spinel.
Con a y o he py oxeni es om he Rio S ega-Mon e P inze a man le bodies, no pa agene ic o
ex u al e idence o he p esence o an ea lie ga ne -bea ing assemblage was obse ed o he Mon e
Ga i man le py oxeni es. Assuming ha he Mg# alue o he clinopy oxene co es om Type-I
py oxeni es was no signi ican ly modi ied by in e ac ion wi h he in il a ing mel s, and no Fe–Mg
subsolidus exchange wi h associa ed ma ic mine als occu ed, we calcula ed he Mg# o he
clinopy oxene equilib ium mel s ollowing he equa ion o Wood and Blundy (1997). Compu ed mel
Mg# (49–64) a e subs an ially lowe han he Mg# o mel s in equilib ium wi h a pe ido i e sou ce.
The high Al con en s obse ed in some clinopy oxene co es o Type-I py oxeni es and he high modal
p opo ion o Al- ich spinel (Fig. 2.8) also indica e ha he py oxeni e- o ming mel s we e
cha ac e ized by low Si/Al a ios (Della-Pasqua e al., 1995). We specula e ha hese mel s o med
by pa ial mel ing o p ecu so ma ic/py oxeni e li hology o o a mixed py oxeni e/pe ido i e sou ce.

33
In summa y, he Mon e San 'Agos ino webs e i es a e s uc u ally and composi ionally simila o
he webs e i es, in places e aining ga ne elics, om he Rio S ega-Mon e P inze a man le bodies
(Mon anini e al., 2006). The Mon e Ga i py oxeni es ha e no appa en analogues in he o he man le
bodies so a desc ibed o he Ex e nal Ligu ian ophioli es, al hough new geochemical da a a e
needed o es ablish hei o igin.
2.6.4. The he e ogenei y o he Ex e nal Ligu ian subcon inen al man le
The man le bodies om he Ex e nal Ligu ian ophioli es ep esen di e en domains o a la ge-
scale subcon inen al man le sec ion ha was a iably a ec ed by e og ession, de o ma ion and
chemical modi ica ions du ing li hosphe ic ex ension and concomi an as henosphe ic ascen in
esponse o he i ing p ocess ha led o opening o he Ju assic Wes e n Te hys (Hidas e al., 2020;
Mon anini e al., 2006; Picca do e al., 2004). Based on he main cha ac e is ics o in es iga ed
Ex e nal Ligu ian man le bodies, we subdi ide his subcon inen al man le sec ion in o h ee main
domain ypes.
1- Plagioclase-bea ing spinel ec oni e domain (ST), ep esen ed by he Su e o man le body (Fig.
2.1). The Su e o lhe zoli es and he enclosed py oxeni es eco d a de o ma ion e en de eloped unde
spinel- acies and high empe a u e condi ions (1000–1050 °C), which yielded po phy oclas ic
ex u es associa ed wi h a pene a i e ec onic olia ion in lhe zoli es (Bo ghini e al., 2011; Rampone
e al., 1995). The Su e o lhe zoli es unde wen mel in il a ion o ming py oxeni ic he e ogenei ies
du ing he ea ly Paleozoic (Bo ghini e al., 2013, 2016). Mel mig a ion and py oxeni e o ma ion
was syn- o la e-kinema ic wi h espec o he spinel- acies de o ma ion and p oduced a localized
me asoma ic imp in in he hos lhe zoli es (see also Bo ghini e al., 2021; Hidas e al., 2020). This
e en was in e ed o ha e occu ed unde ela i ely high p essu e condi ions (>1.5 GPa) based on
he geochemical e idence o a p ima y ga ne -bea ing assemblage in he py oxeni es, which was
comple ely eplaced du ing he subsequen decomp ession e olu ion. The Su e o man le body
p o ides e idence o a plagioclase- acies e-equilib a ion unde s a ic condi ions, in esponse o a
ela i ely cold decomp ession (Hidas e al., 2020). In pa icula , wo ec ys alliza ion s ages we e
ecognized, om 0.6–0.7 GPa and 890–910 °C o 0.4–0.5 GPa and 800–840 °C (Fumagalli e al.,
2017, see Fig. 2.11). In e nal Sm-Nd isoch ons (clinopy oxene-plagioclase-bulk ock) ob ained om
ou py oxeni es ga e an a e age age o 178 ± 8 Ma o he plagioclase- acies ec ys alliza ion
(Bo ghini e al., 2016).
2- Plagioclase myloni e (PM) domain, including he Mon e San 'Agos ino ( his s udy) and he Rio
S ega-Mon e P inze a (Fig. 2.1) man le sec ions. In he lhe zoli es om hese man le bodies, a
ec oni ic ex u e de eloped unde spinel- acies condi ions was widely o e p in ed by a dynamic
34
plagioclase- acies ec ys alliza ion associa ed wi h de elopmen o a pe asi e myloni ic olia ion.
Simila o he lhe zoli es, he enclosed py oxeni es eco d di e en ex en s o spinel- and plagioclase-
acies de o ma ion. Using he mine al chemis y da a epo ed in Mon anini e al. (2006), we ob ained
p essu e and empe a u e es ima es o 0.4–0.5 GPa and 850–870 °C (TCa-in-Opx) o he plagioclase-
acies myloni ic de o ma ion o he Rio S ega-Mon e P inze a lhe zoli es (Table 2.5). These
p essu e- empe a u e e alua ions may be econciled wi h he p essu e- empe a u e e olu ion
ecognized o he Mon e San 'Agos ino man le sec ion (Fig. 2.11), assuming ha he ~0.5 GPa
man le upli in he plagioclase s abili y ield was associa ed wi h a polyphase de o ma ion (Fig. 2.11).
Radiome ic cons ain s on he age o he plagioclase- acies shea ing a ec ing he Rio S ega-Mon e
P inze a man le bodies we e placed by a Lu–H mine al isoch on o 220 ± 13 Ma ob ained om a
ga ne py oxeni e (Mon anini e al., 2006). This isoch on was in e p e ed as a cooling age, implying
ha he ga ne py oxeni e passed h ough he Lu–H blocking empe a u e o 800–900 °C (i.e., unde
plagioclase acies condi ions) a ~220 Ma. Acco dingly, we ela e he polyphase plagioclase- acies
de o ma ion eco ded by he PM man le domain o la ge-scale li hosphe ic shea zones de eloped in
he la e T iassic. An ea ly Ju assic Sm-Nd mine al isoch on o 186 ± 2 Ma (de ined by plagioclase,
clinopy oxene, ga ne and whole- ock) was also acqui ed om he Rio S ega-Mon e P inze a ga ne
py oxeni e, and in e p e ed o e lec a p ocess o slow cooling in he plagioclase s abili y ield
(Mon anini e al., 2006).
3- Plagioclase-imp egna ed domain (PI), ep esen ed by he Mon e Ne o man le body (Fig. 2.1)
and he Mon e Ga i man le sec ion ( his s udy). The o me mainly consis s o weakly olia ed
lhe zoli es cha ac e ized by in e s i ial c ys alliza ion o plagioclase and py oxenes, and ex ensi e
eplacemen o C -spinel by plagioclase (Rampone e al., 1995). Acco ding o Picca do e al. (2004),
he o ma ion o plagioclase in he lhe zoli es was ela ed o eac ion wi h a pe asi ely mig a ing
mel . The applica ion o he FACE geoba ome e (Fumagalli e al., 2017) o (i) plagioclase- acies
g anoblas ic agg ega es, and (ii) ims o la ge o hopy oxenes and clinopy oxenes, and associa ed
plagioclase (da a a e Rampone e al., 1995) yielded p essu es o 0.6–0.7 GPa and TCa-in-Opx o 960-
980 °C (Table 2.5). We also applied he geo he mome e o Liang e al. (2013), based on slowly
di using ace elemen s like a e ea h elemen s and Y, o clinopy oxene-o hopy oxene pai s om
he Mon e Ne o plagioclase- acies g anoblas ic assemblage (Picca do e al., 2004). The ob ained
empe a u es (1120–1140 °C) a e signi ican ly highe han hose eco ded by con en ional py oxene
he mome e s. Such esul s a e consis en wi h imp egna ion by as henosphe ic mel s, ollowed by
slow cooling (Dyge and Liang, 2015) associa ed wi h subsolidus ec ys alliza ion. The in il a ion
o as henosphe ic mel s du ing he i ing- ela ed exhuma ion a Mon e Ne o man le body migh be
ela ed o he local occu ence o cm-scale gabb oic i egula eins (Mon anini e al., 2008). No ably,
35
his man le body also encloses up o me e -scale gabb oic in usions and is in places c osscu by basal
dykes, wi h bo h gabb os and basal s displaying MORB- ype chemical signa u e (Mon anini e al.,
2008). The Sm–Nd clinopy oxene-plagioclase wo-poin alignmen s o 163 ± 20 Ma and 165 ± 20
Ma ob ained by Rampone e al. (1995) p esumably eco d he iming o cooling a e MORB
imp egna ion associa ed wi h plagioclase o ma ion. The Mon e Ne o and Mon e Ga i man le bodies
sha e simila p essu e and TCa-in-Opx es ima es o he e en o mel - ock eac ion unde plagioclase-
acies condi ions (Fig. 2.11), and p o ide no e idence o shea ing in he plagioclase s abili y ield.
Con a y o he Mon e Ne o pe ido i es, howe e , he Mon e Ga i pe ido i e-py oxeni e associa ion
is no in uded by gabb os no is c osscu by basal dikes. New geoch onological cons ain s a e
he e o e equi ed o elucida e i he mel imp egna ion e en eco ded by he Mon e Ga i man le
body occu ed in he Ju assic o du ing a p eceding s age (e.g., la e T iassic) o he i ing e olu ion.
Fig. 2.11 compa es he plagioclase- acies p essu e- empe a u e e olu ion o he man le sec ions
conside ed in his s udy and o he Su e o man le body (Bo ghini e al., 2011; Fumagalli e al., 2017).
I also epo s he p essu e- empe a u e es ima es ob ained in he p esen s udy o he Rio S ega-
Mon e P inze a and he Mon e Ne o pe ido i es. The ST and PM man le domains documen a
ela i ely cold plagioclase- acies his o y cha ac e ized by a signi ican p essu e dec ease. We hus
p opose ha hese domains sha ed a common e olu ion in he la e T iassic-ea ly Ju assic. In his
amewo k, he Su e o man le body ep esen s a nea ly unde o med domain (ST), whe eas
plagioclase- acies s ain localiza ion p oduced he PM man le domain cha ac e ized by ex ensi e
myloni ic de o ma ion (Fig. 2.12).
The PI man le domain eco ds highe plagioclase- acies he mal condi ions han he ST-PM
man le domains (Fig. 2.11). We ela e he dis inc plagioclase- acies he mal g adien s eco ded by
he Ex e nal Ligu ian man le bodies o mel -p esen s. mel -absen condi ions du ing hei
decomp ession his o y in he ex ending li hosphe e. The h ee di e en man le domains we e pa o
a subcon inen al man le sec ion ha was in ol ed in o he de elopmen o an ocean-con inen
ansi ion, owa ds he Ad ia pla e, in he Middle Ju assic (Ma oni e al., 1998; Mon anini e al.,
2006). Tec onic dismembe ing du ing con e gence- ela ed o ma ion o sedimen a y melanges in
Uppe C e aceous (Ma oni e al., 2017) hampe ed he p ese a ion o p ima y ela ionships among
he di e en man le domains. We specula e ha he PI domain enclosing he MOR- ype c us al ocks
(i.e., he Mon e Ne o man le body) was loca ed oceanwa d wi h espec o he ST-PM domains in he
Middle Ju assic.
2.6.5. Cons ain s on he man le e olu ion in he Wes e n Te hys ocean-con inen
ansi ion
36
He e we p o ide a b ie o e iew o he li hosphe ic man le bodies belonging o he ocean-
con inen ansi ional domains o he Wes e n Te hys. In pa icula , we compa e he i ing e olu ion
o he Ex e nal Ligu ian man le sec ion wi h ha in e ed om he in es iga ions ca ied ou o he
subcon inen al man le bodies om Wes e n (Lanzo massi ) and Cen al Alps (Malenco, Pla a and
To alp). Simila o he Ex e nal Ligu ian man le sec ion, hese bodies we e exhumed along he OCT
o he Ad ia ma gin (e.g., Gua nie i e al., 2012; Kaczma ek and Mün ene , 2008; Mana schal and
Mün ene , 2009; Mün ene e al., 2004, 2010). Thei e olu ion om he pos -Va isic o ogenic
collapse o he Mesozoic ex ensional phases and basin opening we e e iewed by Picazo e al. (2016),
who poin ed ou how hei p is ine composi ional he e ogenei y was ampli ied du ing he i ing and
oceaniza ion p ocesses. They p oposed a concep ual model wi h wo main ypes o li hosphe ic
man le sec ions, namely (1) “inhe i ed” and (2) “ e e ilized”, exempli ied by he Malenco-To alp-
Uppe Pla a and he Lowe Pla a bodies, espec i ely. In hei iew, he e e ilized man le is a
subcon inen al man le sec ion loca ed oceanwa ds om he inhe i ed subcon inen al man le.
The inhe i ed man le is domina ed by e ile, amphibole-bea ing spinel pe ido i es, ypically
in e laye ed wi h py oxeni es ha a e in places ga ne -bea ing (Mün ene and He mann, 1996). The
inhe i ed man le is in e p e ed as old li hosphe ic man le ha was benea h he con inen al c us be o e
onse o i ing. This in e p e a ion is suppo ed by he p ese a ion o p ima y con ac s be ween he
Malenco man le body and unde pla ed gabb os o ea ly Pe mian age (He mann e al., 1997; Mün ene
and He mann, 1996). In he inhe i ed pe ido i es, no e idence o plagioclase o ma ion, ei he o
subsolidus o mel - ock eac ion o igin, was epo ed. No ably, he Malenco, To alp and Uppe Pla a
man le bodies a e cha ac e ized by simila esul s o REE-in- wo-py oxene and majo elemen
py oxene he mome e s (850–950 °C, Dyge and Liang, 2015), as expec ed o a slowly cooling,
subcon inen al li hosphe ic man le.
In he e e ilized li hosphe ic man le, which also includes he Lanzo Sou h body (Picazo e al.,
2016), he pe ido i es mainly a e plagioclase-en iched clinopy oxene-poo lhe zoli es (Mün ene e
al., 2004, 2010; Picca do e al., 2007). These ocks enclose: (i) duni e-ha zbu gi e bodies o eplaci e
o igin ha a e up o ens o me e s in scale, and (ii) cm- o m-scale gabb oic eins and dykes (see also
San ilippo e al., 2014, 2019). Py oxene he mome y applied o spinel- acies pe ido i e mine als ga e
equilib a ion empe a u es o 1030–1180 °C (Mün ene e al., 2010), highe han hose calcula ed o
he inhe i ed man le. The plagioclase o ma ion was ela ed o in il a ion o MORB- ype mel s
associa ed wi h c ys alliza ion o new o hopy oxene a e oli ine and/o pa ial eplacemen o
clinopy oxene by o hopy oxene and plagioclase (see also Kaczma ek and Mün ene , 2008). The
e e ilized plagioclase-pe ido i es and he inhe i ed e ile spinel-pe ido i es ha e dis inc mine al
composi ions (Picazo e al., 2016). Fo ins ance, clinopy oxene om he e e ilized pe ido i es has
37
lowe Al2O3 and Na2O han clinopy oxene om he inhe i ed e ile pe ido i es. In addi ion, spinel
has highe C # and TiO2 in he e e ilized pe ido i es han in he inhe i ed e ile pe ido i es.
The Lanzo massi shows a peculia ansi ion om a domain mos ly composed o old inhe i ed
li hosphe ic man le in he no he n pa (e.g., Gua nie i e al., 2012) o a deeply mel -modi ied man le
sec ion in he sou he n pa (Picca do e al., 2007; San ilippo e al., 2014, 2019). The wo domains
a e sepa a ed by a majo shea zone (up o ~1.5 km hick), in which po phy oclas ic pe ido i es
p o ide e idence o plagioclase- acies mel - ock eac ions, in u n o e p in ed by plagioclase
myloni es eco ding solid s a e de o ma ion (e.g., Kaczma ek and Mün ene , 2008; Kaczma ek and
Tommasi, 2011). The myloni es we e in e p e ed as he oo wall o an ex ensional de achmen aul
ha accomoda ed exhuma ion o he Lanzo man le and ac ed as a pe meabili y ba ie be ween he
inhe i ed (no he n Lanzo) and e e ilized (Sou he n Lanzo) domains. We applied he FACE
geoba ome e o he neoblas ic plagioclase-bea ing assemblage o he Lanzo myloni ic pe ido i es
(Kaczma ek and Mün ene , 2008), he eby yielding ema kably low p essu e alues o 0.3 GPa (Table
2.5, Fig. 2.11). These p essu e es ima es a e coupled wi h TCa-in-Opx (B ey and Kohle , 1990) o 840–
870 °C, indica ing a high geo he mal g adien , p esumably ela ed o ex eme li hosphe ic hinning
and as henosphe e ascen . We ob ained sligh ly highe p essu e- empe a u e alues om he
po phy oclas ic pe ido i es o 0.4 GPa and 890 °C sampled along he ma gins o he shea zone.
Picazo e al. (2016) placed he Ex e nal Ligu ian man le bodies in he e e ilized li hosphe ic
man le, because o he widesp ead occu ence o plagioclase-bea ing pe ido i es. Howe e , only some
man le bodies om he Ex e nal Ligu ian uni s include plagioclase o igina ed by eac ion wi h
in il a ing mel s (i.e., he PI domain de ined in he p eceding sec ion). The e e ilized man le o
Picazo e al. (2016) and he Ex e nal Ligu ian PI domain ac ually sha e se e al s uc u al and
composi ional simila i ies, namely: (i) he p esence o mic os uc u es indica ing mel - ock eac ions
in he plagioclase s abili y ield, (ii) he clinopy oxene and spinel composi ion (Figs. 2.6 and 2.7),
and (iii) he ela i ely high empe a u es compu ed o he plagioclase e-equilib a ion (Fig. 2.11).
Con e sely, he Ex e nal Ligu ian plagioclase-bea ing spinel ec oni es and plagioclase myloni es
(ST and PM domains, espec i ely) eco d o ma ion o plagioclase in esponse o subsolidus
decomp ession, wi h no mel in ol emen . Howe e , he econs uc ion o he Ju assic OCT by
Picazo e al. (2016) does no include he occu ence o a plagioclase-bea ing man le sec ion wi h no
mel - ock eac ion e idence.
The e ile spinel pe ido i es conside ed as inhe i ed subcon inen al man le by Picazo e al. (2016)
bea se e al simila i ies wi h he spinel ec oni e and myloni e p o oli hs o he Ex e nal Ligu ian
man le bodies. Taken as a whole, hese pe ido i es a e cha ac e ized by a e ile geochemical
signa u e, p esence o Al- and Na- ich clinopy oxene (Fig. 2.6) and dissemina ed Ti-amphibole.

38
Py oxeni e laye s, in places ga ne -bea ing, a e also widesp ead in bo h man le sec ion ypes.
Following he subdi ision o he Te hyan OCT man le in o wo main ypes (Picazo e al., 2016), we
he e o e place he ST and PM man le domains o he Ex e nal Ligu ian uni s in o he inhe i ed
subcon inen al man le.
The Malenco-To alp-Uppe Pla a man le bodies and he Ex e nal Ligu ian ST and PM man le
domains unde wen dis inc p essu e- empe a u e e olu ions du ing he pos -Va iscan li hosphe ic
ex ension and he subsequen Mesozoic i ing (Fig. 2.11). A cold exhuma ion pa h was depic ed o
he Malenco man le body, conside ed as he ype locali y o inhe i ed man le (Mün ene e al., 2000).
The Malenco pe ido i es unde wen a nea -isoba ic cooling o ~600 °C in he la e Paleozoic, ollowed
by nea -iso he mal decomp ession om ~0.8 o ~0.4 GPa, associa ed wi h o ma ion o chlo i e and
Mg-ho nblende, locally along myloni ic shea zones (see also Mün ene and He mann, 2001). Based
on 40A /39A amphibole in es iga ions (Villa e al., 2000), he decomp ession was in e ed o ha e
s a ed in he la e T iassic (~225 Ma) and was ela ed o he onse o he i ing e olu ion leading o
opening o he Wes e n Te hys.
The Ex e nal Ligu ian PM domain p o ides e idence o a wo-s age high empe a u e
decomp ession s a ing om he base o con inen al li hosphe e (Mon anini e al., 2006). The ea ly
decomp ession om ~2.8 GPa and ~1100 °C o he spinel lhe zoli e s abili y ield was associa ed
wi h cooling o ~950 °C and was ollowed by a polyphase shea ing unde plagioclase- acies
condi ions ending a 0.3–0.6 GPa and 750–780 °C (Fig. 2.11). Whe eas he age o he high
empe a u e decomp ession o spinel- acies lhe zoli e condi ions is uncons ained, he Lu–H cooling
age o 220 ± 13 Ma (Mon anini e al., 2006) indica e ha he spinel o plagioclase- acies ansi ion
was ela ed o he Mesozoic i ing e en (see also §2.6.3). The simila 40A /39A and Lu–H cooling
ages ob ained espec i ely o he Malenco man le body and he Ex e nal Ligu ian PM domain
sugges di e en he mal condi ions in he la e T iassic, namely he Malenco was ~250–300 °C colde
han he Ex e nal Ligu ian PM domain. The dis inc exhuma ion his o ies migh e lec di e en
man le dep hs a he ime o he i ing incep ion. In his iew, he Ex e nal Ligu ian PM domain was
exhumed om deepe (and ho e ) condi ions han he spinel pe ido i es om he Malenco man le
body (Fig. 2.12).
The plagioclase- acies shea zones wi hin he Ex e nal Ligu ian PM domain documen a majo
de o ma ion e en ha accommoda ed exhuma ion o he spinel- acies subcon inen al man le in he
plagioclase s abili y ield. These shea zones canno be conside ed as coun e pa s o hose occu ing
in he cen al Lanzo massi . The po phy oclas ic spinel p o oli hs o he Ex e nal Ligu ian myloni es
do no p o ide e idence o mel in il a ion and e e iliza ion be o e o du ing shea ing. The Lanzo
plagioclase- acies shea zones a e also dis inc o being c osscu by MOR- ype gabb os and basal s.
39
No ably, a ailable geoch onological da a o he eplaci e ha zbu gi es and he gabb os o he Lanzo
Massi clus e in he Middle Ju assic (Kaczma ek e al., 2008; San ilippo e al., 2019). Hence, he
Lanzo shea zones we e mos likely ela ed o an ad anced s age o he i ing e olu ion, which
ul ima ely o med an oceanwa d OCT sec o .
In summa y, he onse o he Te hyan i ing in ol ed upli o subcon inen al man le in he la e
T iassic, as documen ed by he Malenco body (e.g., Mün ene and He mann, 2001) and he Ex e nal
Ligu ian PM domain (Mon anini e al., 2006). This scena io is consis en wi h he in o ma ion
acqui ed om he lowe con inen al c us sec ion o he I ea-Ve bano Zone, which o med a dis al
sec o o he ex ending Ad ia con inen al ma gin in he Middle Ju assic (e.g., Bel ando e al., 2015).
The I ea-Ve bano Zone ac ually documen s ha he i ing e olu ion s a ed in he la e T iassic (see
also Fe a i e al., 2021) and was associa ed wi h localized in il a ion o man le-de i ed mel s wi h
o e all alkaline signa u e (Bonazzi e al., 2020; Schal egge e al., 2015; S ahle e al., 1990). No ably,
he alkaline magma ism in he I ea-Ve bano Zone con inued un il he ea ly Ju assic (see also Galli
e al., 2019 and G ieco e al., 2001). F om he la e T iassic, he i ing e olu ion p obably comp ised
as henosphe e ascen , mel p oduc ion and e e iliza ion o he subcon inen al man le, wi h a Middle
Ju assic climax de eloping MORB- ype mel s and opening o he Wes e n Te hys.
2.7. Conclusions
The subcon inen al man le sec ion om he Ex e nal Ligu ian uni s (No he n Appennine)
consis s o h ee dis inc man le domains, de eloped in esponse o he i ing e olu ion ha ul ima ely
o med a Middle Ju assic ocean-con inen ansi ion: (1) a spinel ec oni e domain ha unde wen no
signi ican de o ma ion and mel - ock eac ion unde plagioclase- acies condi ions, cha ac e ized by
s a ic plagioclase de elopmen unde dec easing p essu e condi ions, (2) a plagioclase myloni e
domain expe iencing mel -absen de o ma ion unde dec easing p essu e condi ions, and (3) a nea ly
unde o med domain ha unde wen mel in il a ion and eac ion unde plagioclase- acies condi ions.
We ela e man le domains (1, 2) o a i ing-d i en upli in he la e T iassic accommoda ed by la ge-
scale shea zones consis ing o plagioclase myloni es.
We dis inguish di e en man le exhuma ion s yles o he onse o he Te hyan i ing. A cold
man le exhuma ion is exempli ied by he Malenco man le body (Cen al Alps), in which low
empe a u e hyd ous myloni es de eloped a he expense o po phy oclas ic spinel lhe zoli es. The
Ex e nal Ligu ian man le domains (1, 2) highligh man le exhuma ion accommoda ed by la ge-scale
shea zones consis ing o anhyd ous, mel -absen plagioclase- acies myloni es. The ole o hese shea
zones in man le exhuma ion along mode n and ossil OCTs has been o e looked and needs u he
econside a ion in u u e s udies. F om he la e T iassic, he Te hyan i ing e olu ion p obably
40
in ol ed as henosphe e ascen , mel p oduc ion and e e iliza ion o he subcon inen al li hosphe ic
man le. The c us al b eakup was associa ed wi h a majo e en o o ma ion o MORB- ype mel s in
he Middle Ju assic, wi h he man le exhuma ion pa ly d i en by a mel -p esen plagioclase- acies
de o ma ion, as documen ed by he Lanzo man le body om Wes e n Alps.
2.8. Re e ences
Basch V., Bo ghini G., Fumagalli P., Rampone E., Gandol o A., Fe ando C., 2020. Plagioclase-
acies he moba ome ic e olu ion o he Ex e nal Ligu ide py oxeni e-bea ing man le (Su e o,
I aly). O ioli i 45, 1-12
Basch V., Rampone E., Bo ghini G., Fe ando C., Zane i A., 2019. O igin o py oxeni es in he
oceanic man le and hei implica ions on he eac i e pe cola ion o deple ed mel s. Con ibu ions
o Mine alogy and Pe ology 174, 97
Beccalu a L., Maccio a G., Picca do G.B. and Zeda O., 1984. Pe ology o lhe zoli ic ocks om he
No he n Apennine ophioli es. Li hos 17, 299-316
Bel ando M., S ockli D.F., Deca lis A. and Mana schal G., 2015. A c us al-scale iew a i
localiza ion along he ossil Ad ia ic ma gin o he Alpine Te hys p ese ed in NW I aly.
Tec onics 34, 1927-1951
Bodinie J.-L., Ga ido C.J., Chane o I., B uguie O. and Ge illa F., 2008. O igin o py oxeni e-
pe ido i e eined man le by e e iliza ion eac ions: E idence om he Ronda pe ido i e
(Sou he n Spain). Jou nal o Pe ology 49, 999-1025
Bonazzi M., Langone A., Tumia i S., Della ole E., Mazzucchelli M., Gio ana di T. and Zane i A.,
2020. Man le-De i ed Co undum-Bea ing Felsic Dykes May Su i e Only wi hin he Lowe
(Re ac o y/Ine ) C us : E idence om Zi con Geochemis y and Geoch onology (I ea-
Ve bano Zone, Sou he n Alps, I aly). Geosciences 10, 281
Bo ghini G., Fumagalli P. and Rampone E., 2010. The S abili y o Plagioclase in he Uppe Man le:
Subsolidus Expe imen s on Fe ile and Deple ed Lhe zoli e. Jou nal o Pe ology 51, 229-254
Bo ghini G., Fumagalli P. and Rampone E., 2011. The geoba ome ic signi icance o plagioclase in
man le pe ido i es: A link be ween na u e and expe imen s. Li hos 126, 42-53
Bo ghini G., Rampone E., Class C., Golds ein S., Cai Y., Cip iani A., Ho mann A.W., Bolge L.,
2021. En iched H –Nd iso opic signa u e o eined py oxeni e-in il a ed pe ido i e as a possible
sou ce o E-MORB. Chemical Geology 586, 120591
41
Bo ghini G., Rampone E., Zane i A., Class C., Cip iani A., Ho mann A.W. and Golds ein S.L., 2013.
Me e -scale Nd iso opic he e ogenei y in py oxeni e-bea ing Ligu ian pe ido i es encompasses
global-scale uppe man le a iabili y. Geology 41, 1055-1058
Bo ghini G., Rampone E., Zane i A., Class C., Cip iani A., Ho mann A.W. and Golds ein S.L., 2016.
Py oxeni e Laye s in he No he n Apennines’ Uppe Man le (I aly)-Gene a ion by Py oxeni e
Mel ing and Mel In il a ion. Jou nal o Pe ology 57,625-653
Bo ghini G., Rampone E., Zane i A., Class C., Fumagalli P., Goda d M., 2020. Ligu ian py oxeni e-
pe ido i e sequences (I aly) and he ole o mel - ock eac ion in c ea ing en iched-MORB man le
sou ces. Chemical Geology 532, 119252
B ey G.P. and Köhle T., 1990. Geo he moba ome y in ou phase lhe zoli es II. New
he moba ome e s, and p ac ical assessmen o exis ing he moba ome e s. Jou nal o Pe ology
31, 1353-1378
Chazo G., Cha pen ie S., Ko np obs J., Vannucci R. and Luais B., 2005. Li hosphe ic Man le
E olu ion Du ing Con inen al B eak-Up: The Wes Ibe ia Non-Volcanic Passi e Ma gin. Jou nal
o Pe ology 46, 2527-2568
Con i P., Co namusini G. and Ca mignani L., 2020. An ou line o he geology o he No he n
Apennines (I aly), wi h Geological Map a 1:250,000 scale. I alian Jou nal o Geosciences 139,
149-194
Della-Pasqua F.N., Kamene sky V.S., Gaspa on M., C aw o d A.J. and Va ne R., 1995. Al-spinels in
p imi i e a c olcanics. Mine alogy and Pe ology 53, 1-26
Dyge N. and Liang Y., 2015. Tempe a u es and cooling a es eco ded in REE in coexis ing
py oxenes in ophioli ic and abyssal pe ido i es. Ea h and Plane a y Science Le e s 420, 151-161
El e P., Ghiselli F., Ma oni M. and O ia G., 1997. No e illus a i e del Foglio 198 "Bobbio" della
Ca a Geologica d'I alia in scala 1:50.000
Fe a i E., T ibuzio R., Bosch D. and B uguie O., 2021. Cons ain s on he pos -Va iscan he mal
e olu ion o he I ea c us al sec ion (I alian-Swiss Alps) om U-Pb da ing o elic u ile in
middle c us amphiboli es. Li hos 406-407, 106500
Fumagalli P., Bo ghini G., Rampone E. and Poli S., 2017. Expe imen al calib a ion o Fo s e i e–
Ano hi e–CaTsche m.ak–Ens a i e (FACE) geoba ome e o man le pe ido i es. Con ibu ions
o Mine alogy and Pe ology 172, 38
48
2.9. Tables
Table 2.1. Summa y o mic os uc u al and mine alogical ea u es o Mon e Ga i and Mon e San 'Agos ino man le ocks
Samples
Li hology
Thickness
Mic os uc u e
Main pe og aphic ea u es
Mon e Ga i man le sequence
Pe ido i es
MGA7
Cpx- ich Spl-Pl
ha zbu gi e
a-
Nea ly iso opic;
coa se-g ained, imp egna ed
E idence o mel - ock eac ion: C -Ti- ich Spl (C #= 33-35, TiO2 =0.3-0.5 w .%)
wi h Pl co onas; Pl + Opx as eplacemen o Cpx
Type Ia py oxeni es
GAV2
Spl webs e i e*
~10-80 cm
Iso opic, coa se-g ained,
g anula allo iomo phic
Coa se Al-Spl (C # = 2-4, TiO2 < 0.10 w %) wi h hin Pl ims
and smalle C -Spl (C # = 12-34, TiO2 = 0.15-1.0 w %);
embayed coa se Cpx wi h Pl + Opx lamellae; Mg# o coa se Cpx = 84-86
Type Ib py oxeni es
GA1, MG6
Spl webs e i e*
~10-80 cm
Iso opic, coa se-g ained,
g anula allo iomo phic
Py oxene- ich (Cpx + Opx + Pl) and Pl- ich (Pl + Ol + C -Spl + Ilm + sul ide)
domains
elic coa se Cpx eplaced by Opx + Pl as ims and lamellae; Mg# o Cpx = 79-85
Type II py oxeni es
MG5, IC2/3,
MG9
Ol-Spl webs e i e*
~10 cm
Iso opic, medium- o coa se-
g ained, g anula
allo iomo phic
Relic exsol ed Opx and Fo- ich Ol (89 mol%) om he hos pe ido i e + Cpx- ich
domains wi h in e s i ial Pl (embayed Cpx wi h lamellae o Pl + Opx); spinels wi h
a iable C # (6-16) and TiO2 (0.1-0.6 w %) immed by Pl
Mon e San 'Agos ino man le sequence
Pe ido i es
MGO1, IC8-1,
IC8-3, IC11
Spl- Pl lhe zoli e
a-
Folia ed, p o omyloni ic
o ul amyloni ic wi h spinel
ec oni e elics
Opx+Cpx (+Spl+Ti-Amp) po phy oclas s in a ul a ine-g ained Ol+Opx+Cpx+Pl
± Amp ± Spl polyphase ma ix; highly s e ched Opx. Al2O3 (7.0-8.4 w %) and Na2O-
ich (1.6-2.1 w %) Cpx po phy oclas s, C -and Ti-poo Spl (C # = 8-16, TiO2 < 0.2
w %)
Py oxeni es
AM489,
MP7, IC10-1
Spl webs e i es
~1-10 cm
P o omyloni ic
Po phy oclas s o Cpx + Opx + Al-Spl se in o a ma ix o Cpx + Opx + Ol + Pl + Ti-
Amp; Opx + Al-Spl + Pl symplec i ic in e g ow hs a e ga ne
* p o oli h be o e mel - ock in e ac ion; sample loca ions a e epo ed in Fig. 2.2

49
Table 2.2. Rep esen a i e majo elemen composi ions (w %) o mine als om Mon e Ga i selec ed samples.
SiO2
TiO2
Al2O3
C 2O3
FeO
MnO
MgO
CaO
Na2O
K2O
NiO
To al
Mg#
C #
An
MGA7 Ha zbu gi e
Ol
40.61
-
-
-
9.57
0.08
49.42
0.09
-
-
0.50
100.27
90
-
-
Opx co e
54.49
0.09
5.40
0.67
7.20
0.11
32.38
0.79
-
-
-
101.12
89
-
-
Opx im
55.48
0.15
3.59
0.79
7.11
0.17
32.79
0.87
-
-
-
100.95
89
-
-
Cpx co e
49.90
0.58
7.29
0.92
3.49
0.06
14.77
21.65
0.88
-
-
99.53
88
-
-
Cpx im
51.66
0.83
4.69
1.13
2.88
-
15.98
22.19
0.75
-
-
100.11
91
-
-
Spl
-
0.50
36.92
28.47
19.30
0.22
14.53
-
-
-
-
99.95
57
34
-
GAV2 Type-Ia py oxeni e
Coa se Cpx co e
48.60
0.77
8.66
0.18
4.73
0.01
13.88
21.92
0.70
-
-
99.45
84
-
-
Coa se Cpx im
51.25
0.67
5.22
0.24
4.50
0.18
15.18
22.74
0.49
-
-
100.47
86
-
-
Small Cpx co e
49.77
0.79
7.41
0.24
4.65
0.30
15.43
21.62
0.66
-
-
100.86
86
-
-
Small Cpx im
51.11
0.80
4.97
0.30
4.54
0.04
15.76
22.74
0.44
-
-
100.69
86
-
-
Al-Spl
-
-
63.43
2.12
15.73
0.14
18.67
-
-
-
-
100.10
71
2
-
C -Spl
-
1.02
32.98
25.40
27.43
-
12.28
-
-
-
-
99.11
53
34
-
GA1 Type-Ib py oxeni e
Py oxene- ich domain
Coa se Cpx1 co e
46.48
2.33
9.71
0.14
6.85
0.12
14.43
17.64
1.73
-
-
99.43
79
-
-
Coa se Cpx2 co e
48.44
2.01
7.88
0.20
5.40
0.20
15.58
17.75
1.40
-
-
98.86
84
-
-
Coa se Cpx2 im
50.46
1.66
6.21
0.13
5.15
0.08
14.61
22.50
0.46
-
-
101.27
83
-
-
Small Cpx
49.24
1.58
6.65
0.11
5.32
0.24
14.23
21.69
0.66
-
-
99.73
83
-
-
Opx ( im o Cpx)
54.62
0.38
2.52
0.07
12.28
0.40
29.01
0.65
-
-
-
99.92
81
-
-
Opx (coa se lamella in Cpx)
54.13
0.50
2.85
0.05
11.65
0.30
29.13
0.95
-
-
-
99.56
82
-
-
Amp
42.57
3.67
12.88
0.38
7.74
0.11
15.21
11.65
3.26
-
-
97.48
78
-
-
Plagioclase- ich domain
Pl
47.89
-
34.01
-
0.33
-
-
15.42
2.30
-
-
99.94
-
-
79
Ol
39.87
-
-
-
17.39
0.30
42.52
-
-
-
0.24
100.32
81
-
-
Spl
-
0.61
35.81
23.16
28.25
0.37
11.00
-
-
-
-
99.20
48
30
-
50
MG6 Type-Ib py oxeni e
Py oxene- ich domain
Coa se Cpx co e
48.79
1.69
7.49
0.12
5.39
0.18
15.45
20.69
0.77
-
-
100.57
84
-
-
Coa se Cpx im
50.23
1.51
5.54
0.11
4.70
0.16
15.54
22.11
0.40
-
-
100.30
85
-
-
Small Cpx
49.67
1.58
6.16
0.19
4.81
-
15.49
21.65
0.52
-
-
100.07
85
-
-
Opx (symplec i e wi h Pl)
54.13
0.40
2.91
0.11
10.99
0.31
30.07
0.96
-
-
-
99.88
83
-
-
Plagioclase- ich domain
Pl
47.42
-
33.70
-
-
-
14.43
2.95
-
-
-
98.50
-
-
73
Ol
39.47
-
-
-
17.59
0.10
43.70
-
-
-
0.19
101.05
82
-
-
Spl
-
0.79
45.02
14.48
26.33
0.15
12.19
-
-
-
-
98.96
51
18
-
IC2/3 Type-II py oxeni e
Ol
40.57
-
-
-
10.63
0.10
48.20
-
-
-
0.40
99.90
89
-
-
Exsol ed Opx
54.71
0.24
5.54
0.55
7.88
0.13
30.46
0.97
0.37
-
-
100.85
87
-
-
Cpx
50.78
1.02
7.41
0.41
3.30
0.18
15.34
22.53
0.56
-
-
101.53
89
-
-
Opx (coa se lamella in Cpx)
55.68
0.26
2.07
0.46
7.44
0.25
33.39
0.72
-
-
-
100.27
89
-
-
Spl
-
0.55
52.49
15.03
15.06
0.24
16.63
-
-
-
-
100.00
66
16
-
Pl
51.82
0.01
31.16
0.05
0.04
-
0.11
13.89
3.70
-
-
100.78
-
-
67
Majo elemen composi ions o mine als we e analysed using a JEOL-6400 elec on mic op obe equipped wi h a LINK-ISIS ene gy dispe si e mic oanaly ical sys em a he Depa men o Chemis y,
Li e Sciences and En i onmen al Sus ainabili y o Pa ma Uni e si y. The elec on beam was p oduced a an accele a ing ol age o 15 kV and p obe cu en o 0.25 nA. Bo h na u al mine als and
syn he ic
compounds we e used as s anda ds. p c=po phy oclas , neo=neoblas , (-) below de ec ion limi (< 0.10 w %). Mine al abb e ia ions a e Whi ney and E ans (2010).
51
Table 2.3. Rep esen a i e majo elemen composi ions (w %) o mine als om Mon e San 'Agos ino pe ido i es
SiO2
TiO2
Al2O3
C 2O3
FeO
MnO
MgO
CaO
Na2O
K2O
NiO
To al
Mg#
C #
An
MGO1 Myloni ic
lhe zoli e
Ol p c
40.97
-
-
-
10.70
0.10
47.95
0.14
-
-
-
99.86
89
-
-
Cpx2 p c co e
51.24
0.42
8.42
0.99
2.70
0.10
14.21
19.60
2.06
-
-
99.74
90
-
-
Cpx p c im
51.63
0.65
5.92
0.85
2.66
-
15.11
22.52
0.93
-
-
100.27
91
-
-
Opx p c co e
54.84
0.33
4.73
0.56
6.65
-
32.83
0.70
-
-
-
100.64
90
-
-
Spl
-
0.15
59.59
9.90
11.55
0.29
18.70
-
-
-
-
100.18
74
10
-
IC8-1 Myloni ic lhe zoli e
Ol p c
41.27
-
-
-
10.31
0.07
48.37
-
-
-
0.49
100.51
89
-
-
Cpx p c co e
50.45
0.48
7.69
1.45
2.60
0.38
13.87
21.25
1.71
-
-
99.88
90
-
-
Opx p c co e
54.87
0.11
4.50
0.44
7.33
0.12
32.12
0.60
-
-
-
100.09
89
-
-
Spl p c co e
-
-
60.90
8.38
11.95
0.02
19.02
-
-
-
-
100.27
74
8
-
Amp
41.54
4.62
14.78
1.20
4.65
0.20
15.14
11.92
4.03
0.10
-
98.18
85
-
-
Ol neo
41.21
-
-
-
9.55
0.14
49.91
-
-
-
0.44
101.25
90
-
-
Cpx neo
52.80
0.51
2.94
0.27
2.75
0.10
17.00
23.20
0.56
-
-
100.13
92
-
-
Opx neo
55.82
0.10
1.62
0.25
7.23
0.32
35.61
0.34
-
-
-
101.29
90
-
-
Pl neo
55.41
-
27.78
-
0.27
-
-
8.75
7.04
-
-
99.25
-
-
41
IC8-3 Myloni ic lhe zoli e
Cpx p c co e
50.65
0.52
8.02
0.55
2.95
0.17
13.83
20.69
1.76
-
-
99.14
89
-
-
Cpx p c im
51.56
0.42
7.39
0.76
2.52
-
14.95
20.46
1.44
-
-
99.51
91
-
-
Opx p c co e
54.59
0.25
5.01
0.44
7.00
0.17
32.10
0.70
-
-
-
100.26
89
-
-
Spl p c co e
-
0.15
57.60
11.43
12.72
0.37
17.91
-
-
-
-
100.18
72
12
-
Amp
42.19
3.59
14.54
1.02
6.00
0.17
17.17
10.91
2.81
0.26
-
98.66
84
-
-
Ol neo
40.84
-
-
-
9.86
0.18
49.31
0.10
-
-
0.30
100.59
90
-
-
Cpx neo
54.41
0.58
3.06
0.62
2.58
-
17.71
22.54
0.70
-
-
102.20
92
-
-
Opx neo
56.71
0.16
1.06
-
7.02
0.2
35.42
0.32
-
-
-
100.89
90
-
-
Pl neo
56.64
-
27.52
-
0.60
-
-
7.75
7.14
-
-
99.64
-
-
38
IC11 ul amyloni ic lhe zoli e
Cpx p c co e
54.75
0.56
6.54
0.83
3.93
0.10
15.14
21.11
1.44
-
-
104.40
87
-
-
Opx p c co e
55.35
0.31
3.65
0.14
6.56
0.22
33.42
0.56
-
-
-
100.21
90
-
-
Spl p c co e
-
-
57.74
10.52
11.93
0.25
19.52
-
-
-
0.36
100.32
76
11
-
Amp p c
43.37
2.42
14.74
0.86
4.24
-
17.17
11.95
3.47
-
98.22
90
-
-
Ol neo
41.04
-
-
-
9.79
0.13
49.73
-
-
-
0.45
101.14
90
-
-
Cpx neo
54.77
0.23
2.23
0.25
2.39
-
17.92
23.37
0.54
101.70
93
-
-
Opx neo
55.70
-
0.74
0.10
7.06
0.14
35.65
0.28
-
-
-
99.67
90
-
-
Pl neo
54.17
-
-
-
0.29
-
-
10.41
5.82
-
-
70.69
-
-
50
52
Spl (neo)
-
-
55.13
10.49
13.47
0.12
20.49
-
-
-
0.28
99.98
80
11
-
p c=po phy oclas , neo=neoblas , (-) below de ec ion limi (< 0.10 w %). Mine al abb e ia ions a e Whi ney and E ans
(2010).
53
Table 2.4. Rep esen a i e majo elemen composi ions (w %) o mine als om Mon e San 'Agos ino py oxeni es
SiO2
TiO2
Al2O3
C 2O3
FeO
MnO
MgO
CaO
Na2O
K2O
NiO
To al
Mg#
C #
An
MP7 Spinel webs e i e
Cpx p c co e
49.64
0.66
9.41
0.23
4.68
0.26
13.40
20.40
1.27
-
-
99.92
84
-
-
Cpx p c im
49.81
0.77
8.33
0.51
3.99
0.15
14.17
20.99
0.97
-
-
99.68
86
-
-
Opx p c co e
51.81
0.13
6.86
0.07
10.67
0.43
28.97
0.62
-
-
-
99.56
83
-
-
Opx p c im
53.52
0.21
4.49
0.19
9.98
0.28
30.49
0.57
-
-
-
99.74
84
-
-
Cpx neo
50.24
0.77
7.33
0.18
5.07
0.20
14.25
21.72
0.77
-
-
100.52
83
-
-
Opx neo
54.30
0.20
2.72
-
11.07
0.36
30.43
0.48
-
-
-
99.57
83
-
-
Spl neo
-
0.09
65.28
1.30
16.58
0.15
17.96
-
-
-
-
101.35
66
1
-
Ol neo
38.42
-
-
-
17.07
0.31
42.79
-
-
-
-
98.59
82
-
-
Pl neo
52.48
-
29.72
-
-
-
-
10.25
4.92
-
-
97.37
-
-
54
Amp
41.32
4.23
14.36
0.64
6.71
0.13
15.06
11.91
2.93
0.45
-
97.74
80
-
-
Opx sym
54.02
0.22
3.57
-
10.91
0.35
30.44
0.52
-
-
-
100.02
83
-
-
Spl sym
-
0.09
63.55
0.74
16.86
0.27
16.95
-
-
-
-
98.46
64
1
-
Pl sym
52.90
-
30.18
-
-
-
-
10.19
5.19
0.18
-
98.64
-
-
52
AM489 Spinel webs e i e
Cpx p c co e
49.79
0.63
9.17
0.34
3.35
0.21
13.51
21.82
0.73
-
-
99.55
88
-
-
Cpx p c im
52.61
0.58
4.42
0.57
2.64
0.15
15.83
23.02
0.52
-
-
100.35
91
-
-
Opx p c co e
54.07
-
6.52
0.23
7.57
0.19
31.40
0.51
-
-
-
100.47
88
-
-
Opx p c im
55.86
-
4.10
0.18
7.65
0.28
32.39
0.55
-
-
-
101.01
88
-
-
Ol neo
40.20
-
-
-
11.71
0.33
47.62
-
-
-
0.21
100.07
88
Cpx neo
50.85
1.26
5.73
3.76
0.21
16.99
21.16
0.67
-
-
100.62
89
-
-
Opx neo
55.40
0.26
2.88
7.41
0.29
33.06
0.67
-
-
-
99.97
88
-
-
Spl neo
-
-
62.50
6.42
13.21
0.45
18.07
-
-
-
-
100.65
71
6
-
Pl neo
52.54
-
30.98
-
-
-
-
10.89
4.93
-
-
99.34
-
-
55
Amp
42.51
5.39
14.99
0.78
5.45
0.28
14.13
11.82
3.29
0.21
-
98.85
83
-
-

54
IC10-1 Spl webs e i e
Cpx p c co e
53.94
0.30
4.75
0.15
-
9.41
0.28
30.58
0.74
100.13
85
Opx p c co e
48.88
0.99
8.41
0.37
-
4.37
0.17
14.70
20.76
1.11
99.76
86
Ol neo
39.86
-
-
-
13.19
0.07
45.16
0.21
-
-
-
98.48
86
Opx neo
55.35
0.23
3.07
0.30
8.56
0.23
32.45
0.69
-
-
-
100.88
87
Cpx neo
50.86
1.05
5.65
0.35
4.00
0.26
15.93
21.92
0.85
-
-
100.86
88
Pl neo
52.93
-
30.06
-
0.47
-
-
10.96
5.06
-
-
99.47
-
54
p c=po phy oclas , neo=neoblas , sym=symplec i e, (-) below de ec ion limi (< 0.10 w %). Mine al abb e ia ions a e Whi ney and E ans (2010).
55
Table 2.5. Geo e moba ome ic es ima es o he Mon e Ga i and Mon e San 'Agos ino man le
sec ions
Mon e Ga i
TCa-in-Opx
TTa98
TBK90
THB94
PFACE (GPa)
Pe ido i es
Exsol ed Opx(1)- Cpx (co e)
950-1110
878-916
897-938
Type I- py oxeni es
Non-exsol ed Opx associa ed wi h Pl (2)
920-1030
Opx - adjacen Cpx in Cpx- ich domain
850-954
876-989
Pl-Amp
1030
0.67-0.78
Type II-py oxeni es
Exsol ed Opx(1)
1001-1047
Non-exsol ed Opx (2) associa ed wi h Pl
910-1065
Opx - adjacen Cpx
970-983
996-1015
0.72
Mon e S. Agos ino
Myloni ic pe ido i es
Po phy oclas ic Opx(1)- Cpx
930-970
832-886
857-950
Neoblas ic Pl-bea ing myloni ic ma ix
(3)
750-780
756-825
788-873
778
0.34-0.55
Spl-Pl webs e i es
Po phy oclas ic Opx(1)- Cpx
920-985
914-958
940-960
Neoblas ic Pl-bea ing ma ix (4)
870-930
856-880
905-938
0.76-0.90
Pl-Amp
880-907
Assumed P o TCa-in-Opx : (1) 1.5 GPa, (2) 0.7 GPa, (3) 0.4 GPa, (4) 0.8
GPa
56
Chap e 3
Insigh s on he Mon e Ga i plagioclase-
acies mel - ock eac ion e en
3.1. In oduc ion
The man le ock bodies om he Ex e nal Ligu ian uni s (No he n Apennines, I aly) eco d
dis inc p essu e- empe a u e e olu ions, as well as de o ma ion p ocesses du ing he Mesozoic
i ing s age ha p eceded he Ju assic Wes e n Te hys opening. A ela i ely cold decomp ession
e olu ion linked o he ex ensional ec onics is widely epo ed o se e al o hese man le bodies.
Exhuma ion o plagioclase- acies condi ions occu ed s a ically in he Su e o man le body (e.g.,
Hidas e al., 2020). Con e sely, he Rio S ega-Mon e P inze a (Mon anini e al., 2006) and Mon e
San ’Agos ino (PhD Thesis, Chap e 2) bodies p o ide e idence o dynamic plagioclase- acies
ec ys alliza ion along hec ome e-scale li hosphe ic shea zones. Fu he mo e, plagioclase- acies
mel - ock eac ion p ocesses a e eco ded by he Mon e Ne o man le body (Picca do e al., 2004).
Plagioclase- acies mel - ock eac ion p ocesses we e also epo ed in his PhD Thesis o he
Mon e Ga i man le body (see Chap e 2). This man le sec ion consis s o ha zbu gi es in e laye ed
wi h spinel py oxeni es le els, which we e subdi ided in o Type-I and Type-II. Because o he mel -
ock in e ac ion e en , bo h pe ido i es and py oxeni es unde wen di e en eplacemen ex en s o :
(i) clinopy oxene, by o hopy oxene + plagioclase, and (ii) spinel, by plagioclase. Type-I py oxeni es
we e subdi ided in wo sub- ypes (Ia and Ib) based on he di e en eplacemen ex en s. In pa icula ,
Type-Ib py oxeni es a e cha ac e ized by (i) py oxene- ich domains in which coa se clinopy oxene
elics a e associa ed o newly o med seconda y o hopy oxene + plagioclase + clinopy oxene, and
(ii) plagioclase- ich domains cons i u ed by plagioclase + oli ine + C -spinel p esumably
ep esen ing he eac ion p oduc s be ween he pe cola ing mel and o iginal Al-spinel- ich domains.
Con e sely, in Type-Ia py oxeni es coa se clinopy oxene and spinel g ains a e well p ese ed, despi e
he local c ys alliza ion o o hopy oxene and plagioclase. Along wi h he pe og aphic e idence,
mine al majo elemen composi ions also egis e s he e ec s o mel imp egna ion. In pa icula , an
inc ease o C # alues (up o 34) and TiO2 con en s (up o 1 w %) is eco ded by spinels om
py oxeni es and enclosing pe ido i es. Mo eo e , eac ed clinopy oxenes om py oxeni es display an
inc ease in TiO2 con en s (up o 2.3 w %). O e all, he pe cola ing mel should ha e been
57
silica(o hopy oxene)-sa u a ed and Ti- ich. Acco ding o he FACE geoba ome e o Fumagalli e
al. (2017), he plagioclase- acies mel - ock eac ion p ocess occu ed a 0.7-0.8 GPa.
The aim o his Chap e is o assess he Mon e Ga i mel imp egna ion e en . New geochemical
da a on whole ocks and mine al phases will gi e addi ional insigh s on he na u e o he pe cola ing
mel . Nd-H iso opic da a om py oxeni e samples will be used o discuss he possible sou ces o his
mel , besides p o iding age cons ain s on he mel - ock eac ion e en .
3.2. Geological and pe ological amewo k
The Alpine-Apennine ophioli es ep esen li hosphe ic emnan s o he Ju assic Wes e n Te hys
basin (also e e ed o as Ligu ian-Piedmon ese basin). Some ophioli es om he Cen al Alps
(Malenco and To alp; Mün ene e al., 2004, 2010) and No he n Apennines (Ex e nal Ligu ian uni s;
Rampone e al., 1995; Mon anini e al., 2006, 2012) expose man le bodies showing a subcon inen al
o igin and we e in e p e ed o be exhumed along he Wes e n Te hys magma-poo ocean-con inen
ansi ion. O he ophioli es om he Alpine-Apennine sys em (e.g. hose om he In e nal Ligu ian
Uni s) show a ini ies wi h oceanic li hosphe e om slow and ul a-slow sp eading idges (San ilippo
and T ibuzio, 2011; T ibuzio e al., 2014).
The Ex e nal Ligu ian (EL) ophioli es occu as slide blocks wi hin La e C e aceous sedimen a y
melanges o med du ing he con e gence phase ha led o he closu e o he Wes e n Te hys basin
(e.g., Ma oni e al., 2017). The cm- o km-sized slide blocks comp ise subcon inen al man le ocks
(e.g., Picca do e al., 2004), Ju assic MOR- ype gabb os and basal s (T ibuzio e al., 2004, 2016;
Mon anini e al., 2008) and associa ed pelagic sedimen s, La e Ca boni e ous-Ea ly Pe mian
g ani oids (Fe a a and Tona ini, 1985) and ma ic g anuli es (Meli e al., 1996).
Man le ocks a e mainly cons i u ed by e ile spinel-plagioclase lhe zoli es (e.g., Rampone e al.,
1995) locally bea ing accesso y amphibole (kae su i e o i anian pa gasi e). Pe ido i es a e in places
in e laye ed wi h ga ne and spinel py oxeni es (Mon anini e al., 2006, 2012; Mon anini and
T ibuzio, 2015; Bo ghini e al., 2016).
As epo ed in he p e ious Chap e 2, he Ex e nal Ligu ian subcon inen al man le sequences
could be g ouped in h ee main domains acco ding o hei i ing- ela ed e olu ion p eceding he
opening o he Ju assic Wes e n Te hys basin. A plagioclase-bea ing spinel ec oni e (ST) domain,
exempli ied by he Su e o sec ion (e.g., Rampone e al., 1995), eco ded a high- empe a u e (1000-
1050 °C) spinel- acies de o ma ion. A subsequen plagioclase- acies ec ys alliza ion occu ed in
Ju assic imes unde mel -absen s a ic condi ions (Bo ghini e al., 2016; Hidas e al., 2020). Two
ec ys alliza ion s ages we e ecognized, om 0.6-0.7 GPa and 890-910 °C o 0.4-0.5 GPa and 800-
840 °C (Fumagalli e al., 2017) and we e asc ibed o he i ing- ela ed decomp ession e olu ion. A
64
deple ion (LaN/SmN = 0.1-0.3) coupled o a iably en iched HREE (GdN/YbN = 0.4-0.9) and no o
weak nega i e Eu anomalies (Eu/Eu* = 0.7-1.1). S ong nega i e S anomalies and small nega i e H
anomalies a e also isible. O hopy oxenes display p og essi ely inc easing concen a ions om
LREE o HREE ( om ~0.01 o ~10 imes chond i ic alues). No composi ional a ia ions we e
obse ed be ween co e and im o py oxenes om bo h lhe zoli es and webs e i es.
3.6. Geo he mome ic es ima es
T ace elemen analyses o py oxenes and plagioclase we e employed o calcula e empe a u es
based on slowly di using elemen s (REE, Y) acco ding o he calib a ions o Liang e al. (2013) and
Sun and Liang (2017). The o me is based on he REE-Y pa i ioning be ween coexis ing
clinopy oxene and o hopy oxene, whils he la e is based on he REE-Y pa i ioning be ween
coexis ing clinopy oxene and plagioclase. The ob ained es ima es a e epo ed in Table 3.4.
Po phy oclas ic clinopy oxene-o hopy oxene pai s om Mon e Ga i ha zbu gi e MGA7 yielded
alues o 1245 ± 90 °C. Calcula ed empe a u es o coa se clinopy oxene and associa ed
o hopy oxene in Type-Ib MG6 py oxeni e e u ned 1278 ± 32 °C. By using he calib a ion o Sun
and Liang (2017) o Type-Ib coa se clinopy oxene g ains and plagioclase, empe a u es o 1257 ±
48 (MG6) and 1170 ± 14 °C (GA1) we e ob ained.
The geo he mome e o Liang e al. (2013) was also applied on he po phy oclas ic
clinopy oxene-o hopy oxene pai s om Mon e San ’Agos ino samples o compa a i e pu poses.
Th ee myloni ic lhe zoli es (MGO1, IC8-1, IC8-3) e u ned a weigh ed a e age empe a u e o 1044
± 43 °C (MSWD = 0.39). The spinel webs e i e AM489 yielded alues o 1103 ± 78 °C.

65
a)
b)
Fig. 3.4. Rep esen a i e Ra e Ea h Elemen composi ions no malized o chond i e (no malizing alues
a e Sun and McDonough, 1989) o clinopy oxene co es om Mon e Ga i (a) pe ido i es and (b)
py oxeni es. Da a om Su e o (Bo ghini e al., 2016, 2020), Rio S ega-Mon e P inze a (Mon anini e
al., 2012; Mon anini and T ibuzio, 2015; Mon anini unpublished da a) and Mon e Ne o (Picca do e al.,
2004) Ex e nal Ligu ian man le sequences a e shown o compa ison. Rep esen a i e clinopy oxene
REE composi ions om Mon e San ’Agos ino sec ion a e also epo ed. No ewo hy, clinopy oxenes
om Mon e San ’Agos ino lhe zoli es ha e REE pa e ns simila o Su e o and Rio S ega-Mon e
P inze a pe ido i es; clinopy oxenes om Mon e San ’Agos ino spinel webs e i es ha e REE pa e ns
compa able o he o he Ex e nal Ligu ian webs e i es.
66
0.1
1
10
100
1000
La Ce S P Nd Z H Sm Eu Gd Tb Dy YHo E Tm Yb Lu
Cpx/chond i e
a)
0.1
1
10
100
1000
La Ce S P Nd Z H Sm Eu Gd Tb Dy YHo E Tm Yb Lu
Cpx/chond i e
b)
Fig. 3.5. Rep esen a i e ex ended incompa ible elemen s composi ions no malized o chond i e
(no malizing alues a e Sun and McDonough, 1989) o clinopy oxene co es om Mon e Ga i (a)
pe ido i es and (b) py oxeni es. Rep esen a i e clinopy oxene REE composi ions om Mon e
San ’Agos ino sec ion a e also epo ed o compa a i e pu poses.
67
4
5
6
7
8
9
10
11
0.05 0.15 0.25 0.35 0.45
Z /Nd
Ce/Y
a)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.05 0.15 0.25 0.35 0.45
H /Nd
Ce/Y
b)
0
5
10
15
20
25
0 0.5 1 1.5
Z /Nd
Ce/Y
c)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.5 1 1.5
H /Nd
Ce/Y
d)
Fig. 3.6. Z /Nd and H /Nd s. Ce/Y plo s o clinopy oxenes om Mon e Ga i (a, b) pe ido i es
and (c, d) py oxeni es. Da a om Mon e San ’Agos ino, Su e o, Rio S ega-Mon e P inze a and
Mon e Ne o man le sequences a e shown o compa ison.
68
0.001
0.01
0.1
1
10
100
La Ce P Nd Pm Sm Eu Gd Tb Dy Ho E Tm Yb Lu
Opx/chond i e
a)
0.001
0.01
0.1
1
10
100
La Ce P Nd Pm Sm Eu Gd Tb Dy Ho E Tm Yb Lu
Opx/chond i e
b)
Fig. 3.7. Rep esen a i e Ra e Ea h Elemen composi ions no malized o chond i e (no malizing
alues a e Sun and McDonough, 1989) o o hopy oxene co es om Mon e Ga i (a) pe ido i es and
(b) py oxeni es. Da a om Mon e San ’Agos ino a e shown o compa ison.
69
Fig. 3.8. Rep esen a i e Ra e Ea h Elemen composi ions no malized o chond i e
(no malizing alues a e Sun and McDonough, 1989) o Mon e Ga i plagioclase om
Type-Ib py oxeni es.
0.1
1
10
100
La Ce P Nd PmSm Eu Gd Tb Dy Ho E Tm Yb Lu
Pl/chond i e

70
3.7. Nd-H iso opic composi ions
Sm-Nd iso ope analyses we e pe o med on 6 whole ock powde s (GAV2, GA1, GA1 Px-Rich
F ac ion, GA1 Pl-Rich F ac ion, MG6, IC2/3) and 4 clinopy oxene sepa a es (GAV2, GA1, MG6,
MG5) om bo h Type-I and Type-II py oxeni e samples. Addi ional Lu-H iso opic composi ions
we e ob ained o he same clinopy oxene sepa a es (Tab. 3.5).
P esen -day 143Nd/144Nd a ios o Type-Ia whole ock and clinopy oxene (sample GAV2) desc ibe
a na ow ange (0.513148 and 0.513133, espec i ely) coupled o simila 147Sm/144Nd a ios (0.27 and
0.22, espec i ely). A posi i e co ela ion be ween 143Nd/144Nd and 147Sm/144Nd a ios is depic ed by
Type-Ib samples (Fig. 3.9) which show a wide ange o 143Nd/144Nd (0.512816-0.513252) and
147Sm/144Nd (0.17-0.50) alues. The lowes Sm-Nd a ios a e displayed by GA1 Plagioclase-Rich
F ac ion. Type-II py oxeni es ha e 143Nd/144Nd and 147Sm/144Nd alues anging om 0.512896 o
0.513166 and om 0.22 o 0.43, espec i ely. Type-II py oxeni e samples plo along he alignmen
desc ibed by Type-Ib samples.
A consis en e o ch on o 210 ± 20 Ma (n = 8; ini ial εNd = +4.25; MSWD = 9.8) was ob ained
by plo ing all Type-Ib and Type-II samples oge he (Fig. 3.10). The ou GA1 samples (whole ock,
Plagioclase-Rich F ac ion, Py oxene- ich F ac ion and clinopy oxene sepa a e) de ine an e o ch on
(Fig. 3.11) which yielded a simila age (217 ± 36 Ma, ini ial εNd = +3.75; MSWD = 9.2).
Type-Ib clinopy oxenes show 176H /177H alues anging om 0.282934 o 0.283008 and
176Lu/177H alues a ying wi hin a small ange (0.03-0.04). Type-II clinopy oxene has 176H /177H
a ios (0.282983) a 176Lu/177H alues (0.03) simila o Type-Ib clinopy oxenes. Type-Ia
clinopy oxene shows highe 176H /177H a ios (0.283339) a nea ly simila 176Lu/177H a ios (0.04)
compa ed o Type-Ib samples.
Ini ial Nd-H composi ions o clinopy oxene sepa a es we e hen compu ed a 210 Ma, which is
he alue e u ned by he Sm-Nd e o ch on de ined by Type-Ib and Type-II py oxeni es. Type-Ib
and Type-II samples show a na ow in e al o εNd(210) alues (+3.97 o +4.18) a εH (210) alues
a ying om +5.29 o +8.80. O e all, he Nd-H iso opic composi ion o he Mon e Ga i py oxeni es
ecalcula ed o he age p o ided by he Sm-Nd e o ch on a e poo ly adiogenic and plo close o
sligh ly below he man le Nd-H a ay (Fig. 3.12). In con as , Type-Ia clinopy oxene GAV2 has
dis inc ly highe εNd(210) (+8.93) and εH (210) (+19.25) alues, alling in he mo e deple ed po ion o
he MORB ield, abo e he man le a ay.
71
Fig. 3.9. Sm-Nd plo o whole ocks and clinopy oxene sepa a es o Mon e Ga i
py oxeni e samples (clinopy oxene sepa a es a e dis inguished by a c oss).
Fig. 3.10. 143Nd/144Nd s. 147Sm/144Nd co ela ion diag am o all Type-Ib and Type-II
py oxeni es. Da a-poin e o ellipses a e 2σ.
72
Fig. 3.11. 143Nd/144Nd s. 147Sm/144Nd co ela ion diag am o GA1 samples. Da a-
poin e o ellipses a e 2σ.
Fig. 3.12. εH -εNd diag am o clinopy oxene sepa a es o Mon e Ga i py oxeni e samples. εH
and εNd alues a e calcula ed a 210 Ma. MORB (da k g ey do s), OIB (ligh g ey do s) and
HIMU ields and he man le Nd-H line a e om S acke (2012). The Deple ed Man le (DM)
alues a e a e Fau e (1986) and G i in e al. (2000).
73
3.8. Discussion
3.8.1. Geochemical esponse o plagioclase- acies mel in il a ion
Mel - ock eac ion in he Mon e Ga i man le sec ion igge ed some majo elemen s
modi ica ions in spinels (C # alues and TiO2 con en s) and clinopy oxenes (TiO2 con en s) om
bo h pe ido i es and py oxeni es (see §2.6.1. Mon e Ga i: a man le sec ion eco ding eac i e mel
in il a ion in he plagioclase s abili y ield, Chap e 2). T ace elemen composi ions o clinopy oxene
bea u he e idence o he mel in il a ion p ocess. Clinopy oxenes om Mon e Ga i ha zbu gi es
display dis inc REE pa e ns compa ed o he clinopy oxenes o he o he Ex e nal Ligu ian
pe ido i es no a ec ed by plagioclase- acies mel imp egna ion (e.g., Su e o, Rio S ega-Mon e
P inze a and Mon e San ’Agos ino man le sequences; Fig. 3.4). In pa icula , Mon e Ga i
clinopy oxenes a e mo e LREE-deple ed and show highe HREE concen a ions. Thei REE pa e ns
also di e om hose o Mon e Ne o pe ido i es, he o he Ex e nal Ligu ian plagioclase-imp egna ed
man le domain (see §2.6.4. The he e ogenei y o he Ex e nal Ligu ian subcon inen al man le,
Chap e 2). This sugges s ha he Mon e Ga i and Mon e Ne o man le sec ions in e ac ed wi h
geochemically dis inc mel s.
Clinopy oxenes om Mon e Ga i pe ido i es es i y he mel - ock eac ion e en also in ha ing
ela i ely high Z con en s coupled wi h ela i ely low S con en s (Fig. 3.13). Following Mün ene
e al. (2010), who s udied plagioclase pe ido i es om he Lowe Pla a uni , he high Z /S a ios o
Mon e Ga i clinopy oxenes canno be explained by a pe ido i e mel ing model. Ins ead, hey a e
consis en wi h e e iliza ion models, i.e. in e ac ion wi h an in il a ing mel . The plagioclase-
imp egna ed Mon e Ne o pe ido i es ollow his end as well, whils he o he Ex e nal Ligu ian
pe ido i es gene ally exhibi highe S con en s coupled wi h lowe Z con en s.
Mon e Ga i Type-I and Type-II py oxeni es eco ded di e en ex en s o mel - ock in e ac ion.
Speci ically, ex u al and mine al majo elemen s e idence indica e ha Type-Ia py oxeni es we e
no signi ican ly a ec ed by eac ion wi h a pe cola ing mel (see §2.6.1. Mon e Ga i: a man le
sec ion eco ding eac i e mel in il a ion in he plagioclase s abili y ield, Chap e 2). The e o e, he
REE pa e ns o Type-Ia clinopy oxenes p esumably ep esen he composi ion p io o mel - ock
eac ion. Mel imp egna ion ex ensi ely modi ied he REE composi ions o Type-Ib and Type-II
clinopy oxenes, p oducing s ong deple ions in LREE, ma ked Eu anomalies and HREE en ichmen s
(Fig. 3.4). Type-Ib and Type-II clinopy oxenes sha e analogous pa e ns, implying ha he wo
dis inc ypes o Mon e Ga i py oxeni es eac ed wi h he same pe cola ing mel . Such clinopy oxene
REE pa e ns a e no displayed by he o he Ex e nal Ligu ian py oxeni es (Fig. 3.4). The geochemical
80
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T ibuzio R., Renna M.R., Dallai L. and Zane i A., 2014. The magma ic-hyd o he mal ansi ion in
he lowe oceanic c us : Clues om he Ligu ian ophioli es, I aly. Geochimica Cosmochimica
Ac a, 130:188-211
T ibuzio R., Thi lwall M. and Vannucci R., 2004. O igin o he Gabb o---Pe ido i e Associa ion om
he No he n Apennine Ophioli es (I aly). Jou nal o Pe ology, 45:1109-1124
83
Villa I.M., He mann J., Mün ene O. and T ommsdo V., 2000. 39A −40A da ing o mul iply zoned
amphibole gene a ions (Malenco, I alian Alps). Con ibu ions o Mine alogy and Pe ology, 140:
363-381
84
3.11. Tables
Table 3.1. Bulk ock majo and ace elemen composi ions o Mon e Ga i py oxeni es. Majo elemen composi ions a e calcula ed on anhyd ous
basis and no malized o 100. Majo elemen s a e exp essed in w %, ace elemen s in ppm.
Sample
GAV2
GA1
GA1 Pl ich ac ion
GA1 Cpx ich ac ion
MG6
MG5
IC2-3
Desc ip ion
Type Ia py oxeni e
Type Ib py oxeni e
Type Ib py oxeni e
Type Ib py oxeni e
Type Ib py oxeni e
Type II py oxeni e
Type II py oxeni e
SiO2
41.77
46.95
45.29
50.23
47.30
40.84
46.11
TiO2
0.25
0.42
0.14
0.82
0.48
0.38
0.37
Al2O3
14.02
14.44
20.66
11.04
14.06
12.27
7.09
FeO
6.92
8.58
7.03
7.09
8.84
7.49
7.77
MnO
0.14
0.16
0.12
0.20
0.17
0.16
0.13
MgO
24.17
20.04
15.74
18.73
19.02
32.82
30.10
CaO
12.50
6.99
7.82
10.06
7.47
5.92
8.21
Na2O
0.15
0.54
0.82
0.63
0.49
0.10
0.19
K2O
0.09
1.88
2.37
1.20
2.18
0.01
0.02
P2O5
bdl
bdl
bdl
bdl
bdl
0.01
bdl
LOI
8.46
4.12
4.2
2.18
4.04
11.11
7.03
Mg#
86
81
80
82
79
89
87
SiO2/MgO
1.73
2.34
2.88
2.68
2.49
1.24
1.53
V
115
155
76
273
198
155
129
C
2570
790
890
650
620
3300
2400
Ni
900
560
620
260
530
990
1420
Co
53
54
56
35
52
55
69
Sc
17
36
6.00
71
39
35
22
S
15
84
118
61
92
9.00
16
Y
4.90
14
1.20
35
16
9.80
8.40
Nb
bdl
bdl
bdl
bdl
bdl
bdl
bdl
Z
10
20.00
3.00
59.00
21.00
15.00
17.00
La
0.37
0.23
bdl
0.19
0.47
0.22
0.33
85
Ce
1.40
0.93
0.66
1.37
1.31
0.99
1.46
P
0.22
0.20
0.12
0.37
0.26
0.18
0.29
Nd
1.26
1.54
0.76
3.51
1.88
1.12
1.81
Sm
0.48
1.03
0.22
2.45
1.22
0.51
0.66
Eu
0.23
0.46
0.39
0.74
0.49
0.26
0.29
Gd
0.74
1.79
0.27
4.56
2.14
1.00
1.11
Tb
0.13
0.39
0.04
0.93
0.42
0.22
0.22
Dy
0.92
2.50
0.22
6.28
2.90
1.57
1.45
Ho
0.19
0.53
0.04
1.29
0.60
0.37
0.31
E
0.52
1.48
0.11
3.56
1.76
1.10
0.91
Tm
0.08
0.22
0.02
0.51
0.24
0.18
0.14
Yb
0.56
1.39
0.11
3.08
1.69
1.17
1.02
Lu
0.09
0.21
0.02
0.48
0.26
0.18
0.16
H
0.30
0.70
bdl
1.50
0.70
0.40
0.50
Ta
bdl
bdl
0.13
0.01
bdl
bdl
bdl
Th
bdl
bdl
bdl
bdl
bdl
bdl
bdl
U
bdl
bdl
bdl
0.01
0.09
bdl
bdl
LOI = Loss On Igni ion
Mg# = [100 × Mg/(Mg+Fe o )]
bdl = below de ec ion limi s

86
Table 3.2. Rep esen a i e ace elemen composi ions (ppm) o mine als om Mon e Ga i selec ed samples.
Sample
MGA7
GAV2
GA1
MG6
MG5
Rock ype
Ha zbu gi e
Type-Ia py oxeni e
Type-Ib py oxeni e
Type-Ib py oxeni e
Type-II
py oxeni e
Mine al
Opx
Cpx
Cpx
(co e)
Cpx
( im)
Cpx
(co e)
Cpx
(in )
Cpx
( im)
Pl
Cpx
(co e)
Cpx
( im)
Opx
Pl
Cpx (co e)
Sc
28
64
40
45
148
138
220
1.58
154
199
69
3.34
199
Ti
1100
4400
3871
3499
11197
11343
10945
345
10499
9850
3556
553
10233
V
137
312
259
247
543
493
687
2.21
750
867
402
23
491
C
3570
6064
2279
2586
757
726
952
bdl
673
1048
628
24
3605
Co
51
22
26
24
24
24
22
0.08
24
23
63
0.80
17
Ni
bdl
bdl
275
274.57
190
198.61
169
0.67
189
166
348
3.84
265
Rb
bdl
bdl
0.08
0.08
0.03
bdl
bdl
0.06
0.05
0.05
0.06
0.09
0.09
S
0.06
7.61
8.20
7.34
1.53
1.20
1.06
25
1.88
1.89
0.38
40
2.72
Y
2.77
31
16
15
123
128
126
1.10
84
90
7.91
1.75
104
Z
4.36
49
29
27
189
191
221
bdl
126
142
10
1.33
178
Nb
bdl
bdl
0.25
0.16
0.04
0.02
bdl
bdl
0.03
0.02
bdl
bdl
0.02
Ba
bdl
bdl
0.51
1.00
0.11
0.07
0.04
0.16
0.10
0.05
0.18
0.27
0.22
La
bdl
0.47
0.69
0.50
0.26
0.25
0.18
0.24
0.24
0.20
0.01
0.15
0.48
Ce
0.03
3.34
3.72
3.15
2.69
2.65
2.39
0.96
2.57
2.23
0.02
0.90
3.91
P
0.01
0.87
0.76
0.65
1.00
1.17
0.97
0.18
0.93
0.89
0.01
0.19
1.23
Nd
0.10
6.36
4.77
3.95
11
11
11
0.96
9.19
9.32
0.12
1.26
11
Sm
0.07
2.90
1.75
1.53
9.23
9.04
8.76
0.23
6.13
6.31
0.14
0.38
7.42
Eu
0.04
1.11
0.79
0.67
2.29
2.23
2.02
0.62
1.73
1.80
0.03
0.60
1.72
Gd
0.20
4.19
2.49
2.42
16
17
17
0.29
11
12
0.42
0.33
13
Tb
0.05
0.77
0.47
0.42
3.47
3.40
3.54
0.05
2.33
2.46
0.11
0.06
2.79
Dy
0.39
5.42
3.00
2.87
23
24
26
0.22
15
17
1.03
0.26
20
Ho
0.09
1.12
0.61
0.57
4.95
5.10
5.00
0.04
3.30
3.46
0.27
0.08
4.54
E
0.34
3.17
1.66
1.59
13
13
13
0.09
8.56
9.23
1.14
0.16
12
Tm
0.06
0.45
0.24
0.23
1.74
1.78
1.72
bdl
1.21
1.26
0.18
0.04
1.62
Yb
0.55
2.75
1.67
1.47
11
11
11
bdl
7.99
8.18
1.82
bdl
10
87
Lu
0.09
0.38
0.25
0.22
1.39
1.50
1.43
bdl
1.08
1.06
0.34
0.04
1.37
H
0.13
1.38
0.91
0.79
5.26
3.80
7.91
bdl
4.51
6.54
0.469
bdl
6.72
Ta
bdl
bdl
0.05
0.11
0.04
0.01
bdl
0.06
0.03
0.05
0.11
0.21
0.02
Pb
bdl
bdl
0.04
bdl
0.03
bdl
0.03
bdl
0.04
0.03
0.03
bdl
0.07
Th
bdl
bdl
0.03
bdl
0.01
bdl
bdl
bdl
0.01
0.02
bdl
bdl
0.02
U
bdl
bdl
0.01
0.02
0.02
bdl
bdl
0.02
0.01
bdl
bdl
bdl
0.01
LaN/SmN
-
0.10
0.25
0.21
0.02
0.02
0.01
0.69
0.03
0.02
0.04
0.26
0.04
GdN/YbN
0.31
1.26
1.23
1.36
1.20
1.24
1.27
-
1.11
1.18
0.19
-
1.02
Eu/Eu*
1.00
0.97
1.15
1.06
0.57
0.55
0.51
7.29
0.65
0.64
0.43
5.12
0.54
bdl = below de ec ion limi s
88
Table 3.3. Rep esen a i e ace elemen composi ions (ppm) o mine als om Mon e San 'Agos ino selec ed samples.
Sample
MGO1
IC8-1
IC8-3
AM489
Rock ype
Myloni ic lhe zoli e
Myloni ic lhe zoli e
Myloni ic lhe zoli e
Spl webs e i e
Mine al
Opx
(co e)
Opx
( im)
Cpx
(co e)
Cpx
( im)
Opx
(co e)
Cpx
(co e)
Cpx
( im)
Opx
(co e)
Cpx
(co e)
Opx
(co e)
Cpx1
(co e)
Cpx1
( im)
Cpx2
(co e)
Cpx2
( im)
Sc
19
20
65
65
21
91
71
15
55
35
81
89
99
123
Ti
952
836
3689
4021
815
5872
4057
835
4187
728
3181
3425
3252
3468
V
102
99
254
254
101
366
283
93
293
161
341
348
273
280
C
2468
2138
5246
5040
1780
5599
5308
2261
4253
1136
1869
1492
1356
1188
Co
bdl
bdl
bdl
bdl
56
106
24
55
22.99
49
18
15
15
16
Ni
bdl
bdl
bdl
bdl
670
1978
371
677
356
396
169
136
179
180
Rb
bdl
bdl
bdl
bdl
0.18
0.22
0.06
0.07
0.05
0.23
0.18
0.08
bdl
0.08
S
0.22
0.10
60
66
0.67
67
77
0.47
69.57
0.50
5.25
3.95
6.42
6.00
Y
1.24
1.19
18
19
1.29
28
22
1.05
18.61
2.23
29
32
42
43
Z
1.78
1.57
30
32
2.21
54
48
1.83
41.65
2.49
30
35
37
40
Nb
0.01
0.01
0.15
0.10
0.02
0.38
0.05
0.01
0.12
0.01
0.40
0.35
0.32
0.34
Ba
0.004
0.01
0.01
0.005
0.14
0.56
3.92
0.02
0.04
1.01
0.40
0.54
0.28
0.58
La
0.002
0.001
0.87
0.90
0.03
1.68
1.74
0.01
1.50
0.03
0.58
0.42
0.63
0.70
Ce
0.01
0.01
3.15
3.20
0.04
5.71
5.20
0.03
5.34
0.03
2.96
2.85
3.64
3.44
P
0.003
0.002
0.62
0.62
0.02
1.11
0.90
0.01
0.94
0.01
0.67
0.68
0.72
0.72
Nd
0.02
0.02
3.87
3.98
0.10
6.17
5.58
0.05
5.73
0.09
4.65
4.82
4.93
4.82
Sm
0.02
0.02
1.60
1.59
bdl
2.56
2.05
0.03
2.09
bdl
2.20
2.10
2.19
2.21
Eu
0.01
0.01
0.65
0.66
bdl
1.06
0.84
0.01
0.93
0.03
0.88
0.90
0.63
0.74
Gd
0.05
0.04
2.27
2.43
0.08
3.43
3.00
0.07
2.74
0.11
3.28
3.29
3.49
3.24
Tb
0.01
0.01
0.44
0.46
0.02
0.76
0.55
0.01
0.52
0.03
0.64
0.67
0.78
0.85
Dy
0.15
0.14
3.19
3.44
0.14
4.70
3.80
0.09
3.41
0.23
4.60
4.72
7.25
7.17
Ho
0.04
0.04
0.68
0.72
0.04
1.12
0.79
0.04
0.72
0.07
1.07
1.19
1.72
1.69
E
0.18
0.18
2.04
2.08
0.19
3.36
2.41
0.15
2.00
0.36
3.19
3.68
4.97
5.02
Tm
0.04
0.04
0.28
0.32
0.04
0.43
0.34
0.03
0.27
0.07
0.50
0.56
0.76
0.79
Yb
0.29
0.33
1.91
2.14
0.39
3.08
2.25
0.24
2.08
0.58
3.51
3.86
5.60
5.47
89
Lu
0.05
0.06
0.27
0.29
0.09
0.45
0.39
0.04
0.29
0.12
0.52
0.55
0.82
0.79
H
0.06
0.05
0.89
1.00
0.10
1.61
1.24
0.08
1.21
0.10
0.69
0.92
0.91
1.27
Ta
0.02
0.01
0.02
0.02
0.02
0.09
0.04
0.01
0.03
0.02
0.04
0.02
0.05
0.03
Pb
0.09
0.08
0.05
0.05
bdl
0.08
bdl
0.01
0.06
0.55
0.23
0.22
0.15
0.26
Th
0.0002
0.0004
0.03
0.02
0.02
0.06
bdl
0.01
0.03
0.01
0.03
0.06
0.05
0.11
U
0.0003
0.0003
0.01
0.005
0.02
0.03
bdl
0.01
0.03
0.02
0.04
0.03
0.03
0.04
LaN/SmN
0.06
0.05
0.35
0.36
-
0.42
0.55
0.21
0.46
-
0.17
0.13
0.19
0.21
GdN/YbN
0.14
0.11
0.98
0.94
0.17
0.92
1.10
0.25
1.09
0.15
0.77
0.70
0.52
0.49
Eu/Eu*
0.83
0.92
1.04
1.03
-
1.09
1.03
0.94
1.19
-
1.00
1.05
0.69
0.85
bdl = below de ec ion limi s
96
4.3. Field ela ionships and sampling
Samples we e collec ed in he Ouassé Bay, in he Bogo a Peninsula shea zone (Fig. 4.1). The
Bogo a Peninsula is loca ed in he cen al-eas e n pa o he New Caledonia island and ep esen s he
no h-wes e n ex ension o he Massi du Sud.
The Bogo a Peninsula Shea Zone (BPSZ) is a 25-km-wide egion o man le ha zbu gi es
cha ac e ized by a s ain g adien inc easing owa ds wo dis inc 1 o 3 km-wide myloni ic zones
(loca ed in Ouassé and eas o Kouaoua, espec i ely). Localiza ion o de o ma ion is ma ked by
coa se g anula ex u es anging om p o omyloni e o myloni e, oli ine g ain size educ ion,
inc easingly s e ched o hopy oxene g ains (aspec a io up o 25:1) and p esence o oli ine- ich
bands conco dan o he olia ion (Ti us e al., 2011; Cha za as e al., 2020). S ain inc ease also
in luenced ab ic o ien a ion, o a ing s ike olia ion om NW-SE o NNE-SSW and s eepening i
om ~ 60° o ~ 90°. Fo compa ison, he a e age olia ion o he unde o med po ion o he Massi
du Sud body is ~ 20° E-W o NW-SE (Ti us e al., 2011). Dex al sense o mo ion was a ibu ed o
he BPSZ and myloni e zones we e ega ded as he man le a eas co esponding o single aul s in a
ans o m sys em (P inzho e and Nicolas, 1980; Ti us e al., 2011). Cha za as e al. (2020) iden i ied
mic ode o ma ion zones (MDZs) in all de o med ha zbu gi es. MDZs a e µm- o mm-wide and a e
made by ec ys allized oli ine o o hopy oxene locally disloca ing g ains o he p ima y mine al
assemblage. MDZs we e in e p e ed o eco d s ess change h ough ime, om seismic- ela ed b i le
de o ma ion o duc ile de o ma ion and dynamic ec ys alliza ion. In e s i ial pa gasi e modally
inc easing owa ds he myloni e zones sugges s high- empe a u e luids pe cola ing he shea zone,
likely a ou ing s ain localiza ion and myloni iza ion. Se pen ini e shea zones conco dan wi h he
high- empe a u e olia ion would indica e ocean wa e in il a ion du ing cooling o he shea zone
(Teyssie e al., 2016).
P inzho e and Nicolas (1980) i s epo ed he exis ence o se e al dikes in he BPSZ. Based on
c osscu ing ela ionships, he sequence o in usion is (i) py oxeni e, (ii) eldspa hic py oxeni e, (iii)
ho nblende gabb o, (i ) plagiog ani e and ( ) diabase, om he oldes o he younges . A ca e ul
s uc u al s udy o py oxeni e and diabase dikes was made by Ti us e al. (2011). Some py oxeni ic
bodies show cons an hicknesses while o he s a e necked o boudinaged. Locally, he e a e also
olded laye s. Py oxeni e olia ion o a ed and s eepened wi h inc easing s ain, i.e. going owa ds he
myloni e zone, and he dikes unde wen g ea e s e ching. Ul a-elonga ed boudins we e locally
dismembe ed lea ing elic o hopy oxene blebs. Diabase dikes a e mainly ound in he myloni e
zone. Due o hei unde o med na u e, hey we e conside ed as he las magma ic e en .

97
In he Ouassé Bay, po phy oclas ic o myloni ic ha zbu gi es cu by py oxeni ic dikes c op ou .
Up o 1 cm-sized aligned and/o s e ched o hopy oxene g ains de ine he pe ido i e olia ion. Tiny
black spinel is also isible (Fig. 4.2a-b). Py oxeni es occu as 5-15 cm hick laye s, mos ly
in e sec ing a high angle he ha zbu gi e olia ion and showing sha p con ac s (Fig. 4.2c-d).
Disco dan low angle (Fig. 4.2e) and a e conco dan (Fig. 4.2 ), locally boudinaged, laye s occu
oo. Ou sampling ocused on py oxeni es and he hos ha zbu gi es. He e, we epo da a o h ee
webs e i es ( wo disco dan high angle: OU1 and OU4; one disco dan low angle: OU7B), wo
o hopy oxeni es (one conco dan : OU5A; one disco dan high angle: OU8) and h ee ha zbu gi es.
4.4. Me hodology
Majo elemen composi ions o mine als we e analysed using a JEOL-6400 elec on mic op obe
equipped wi h a LINK-ISIS ene gy dispe si e mic oanaly ical sys em a he Depa men o
Chemis y, Li e Sciences and En i onmen al Sus ainabili y o Pa ma Uni e si y. The elec on beam
was p oduced a an accele a ing ol age o 15 kV and p obe cu en o 0.25 nA. Bo h na u al mine als
and syn he ic compounds we e used as s anda ds.
Whole ock powde s we e p epa ed o analyse majo and ace elemen composi ions. Be o e
making he powde s, al e a ion was ca e ully emo ed om each ock sample using he diamond saw.
Then, each ock sample was g ound wi h a mo a un il eaching a size less han 2 mm. The ob ained
g anula e was educed o powde (g ain size < 2 µm) using an aga e mill. The mo a , he sie es and
he aga e mill we e cleaned wi h wa e and alcohol be ween one sample and ano he o a oid any
con amina ion. Whole ock majo and ace elemen s we e analysed a Ac i a ion Labo a o ies
(Ancas e , On a io, Canada) by induc i ely coupled plasma (ICP) op ical emission spec oscopy and
ICP mass spec ome y. P ecision and accu acy a e es ima ed o be be e han 2% o SiO2, Al2O3,
Fe2O3 and MgO and be e han 5% o he o he majo elemen s. P ecision and accu acy o ace
elemen analyses a e assessed o be wi hin 10%.
In si u ace elemen analyses o mine al phases we e ca ied ou using lase abla ion ICP mass
spec ome y a Is i u o di Geoscienze e Geo iso se - C.N.R., Uni à di Pa ia. The lase p obe consis ed
o a Q-swi ched Nd:YAG lase , model Quan el (B illian ), whose undamen al emission in he nea -
IR egion (1064 nm) was con e ed in o 266 nm wa eleng h using h ee ha monic gene a o s (Je ies
e al., 1998). Spo diame e was ypically ~50 µm. The abla ed ma e ial was analysed by using an
Elan DRC-e quad upole mass spec ome e . Helium was u ilized as ca ie gas and mixed wi h A
downs eam o he abla ion cell. NIST 612 was used as ex e nal s anda d. The CaO con en
de e mined by elec on mic op obe was u ilized as in e nal s anda d, scaled on he 44Ca+ signal.
P ecision and accu acy we e assessed om epea ed analyses o he BCR2 s anda d and esul ed
98
be e han 10% a ppm concen a ion le el. De ec ion limi s we e ypically in he ange o 1.0-0.5
ppm o C and Ti, 0.5-0.1 ppm o Sc, 100-10 ppb o S , Z , Ba, Rb, V and Gd, 10-1 ppb o Y, Nb,
REE, H and Ta.
Amphibole sepa a es om wo dis inc amphibole-bea ing webs e i es (OU1 and OU7B) we e
ob ained in o de o ge 40A /39A da a. A e g inding and sie ing o ock samples, amphiboles we e
sepa a ed om he 250/180 µm g anula e ac ions by handpicking.
The 40A /39A analy ical da a a e o ganized o comply wi h FAIR da a epo ing no ms (see o
ins ance Schaen e al., 2020). Each amphibole sepa a e was i adia ed a he O egon S a e Uni e si y
o 14 hou s in he CLICT posi ion. Fish Canyon sanidine was used as he neu on lux moni o and
has an assigned an age o 28.201 Ma (Kuipe e al., 2008) using a 40K decay cons an o 5.463e-10/a
(Min e al., 2000).
A e i adia ion, he sample was s ep-hea ed wi h a diode lase wi h a hea ing ime o 45 seconds pe
s ep ollowed by 45 seconds o gas clean up wi h a SAES GP-50 ge e ope a ed a 2 A. Gas was also
exposed o a cold inge ope a ed a ~-140°C. A gon iso opes we e measu ed using a The mo-Fishe
Scien i ic Helix MC-plus mul i-collec o mass spec ome e . Iso opes 40A , 39A , 38A and 37A we e
measu ed on Fa aday collec o s wi h 40A and 37A using a 1012 Ohm esis o , 39A using a 1013
Ohm esis o , and 38A using a 1014 Ohm esis o . 36A was measu ed on a compac disc e e dynode
(CDD) ion coun e ha has a dead ime o 20 ns. Due o he low K/Ca o he ho nblende, CaF2 was
analysed a he same ime as he sample o help ensu e accu a e co ec ion o p oduc ion o 36A and
39A om i adia ion o Ca.
Calib a ion gases o ai and a gas mix u e en iched in adiogenic 40A along wi h 39A we e analysed
in e spe sed wi h he sample o moni o ins umen d i and de e mine de ec o in e calib a ion
ac o s. Ex ac ion line blanks we e analysed be o e and a e da a collec ion and a e epo ed in he
in ensi y da a wo kshee . All da a collec ion was conduc ed wi h he in-house Pych on so wa e and
da a educ ion u ilized MassSpec e sion 7.875.
The epo ed pla eau age is de i ed om he weigh ed mean o he chosen s eps wi h he weigh ing
ac o being he in e se a iance (e.g., Taylo , 1982) and he e o is he squa e oo o he sum o
1/σ2 alues. The pla eau age e o is epo ed a 1σ and includes he J- ac o e o and i adia ion
co ec ion ac o unce ain ies.
99
Fig. 4.2. Ouassé ou c op. (a,b) Ha zbu gi es wi h ounded o s e ched o hopy oxene po phy oclas s
( ed ci cles) and iny black spinel g ains (blue ci cle). (c,d) Disco dan high angle py oxeni es The hin
whi ish eins a e made o se pen ine. (e) Disco dan low angle py oxeni e. ( ) Conco dan py oxeni e.
100
4.5. Pe og aphy and mine alogy
Rep esen a i e mine al majo elemen composi ions a e lis ed in Table 4.1.
4.5.1. Ha zbu gi es
The s udied ha zbu gi es consis s o 70-80 ol% oli ine, 20-30 ol% o hopy oxene (ens a i e)
and accesso y C -spinel. Tex u es ange om po phy oclas ic o myloni ic (Fig. 4.3a-b). The olia ion
is de ined by aligned and/o s e ched o hopy oxene, wi h aspec a io up o 12:1 (Fig. 4.3c) and
oli ine po phy oclas s.
Oli ine and o hopy oxene po phy oclas s ha e e ac o y composi ions (Fo = 91-92 mol% and
Mg# = 91-92, espec i ely). Up o 1 cm-sized o hopy oxene po phy oclas s locally show undulous
ex inc ion and bending. Thin exsolu ion lamellae o clinopy oxene a e also p esen . O hopy oxene
is cha ac e ised by ela i ely low Al2O3 con en s (1.3-1.9 w %; Fig. 4.6), sligh ly diminishing owa ds
he im (1.1-1.8 w %). C 2O3 and CaO con en s show a b oad dec ease om co e o im (0.6-0.8 o
0.3-0.6 w % and 0.6-1.1 o 0.4-0.7 w %, espec i ely). Up o 1.5 mm da k b own o black spinel
g ains ha e anhed al o subhed al shapes and a e locally o ganised in ails (Fig. 4.3d) conco dan o
he pe ido i e olia ion. They ha e C # and Mg# anging be ween 55-65 and 38-54 (Fig. 4.8),
espec i ely, and low TiO2 con en s (≤0.13 w %).
Po phy oclas s a e se in o a neoblas ic ma ix made o ine-g ained (mos ly 100-400 µm) oli ine
+ o hopy oxene ± spinel displaying a polygonal ex u e. Neoblas ic oli ine has 91-93 mol%
o s e i e. O hopy oxene neoblas s a e mainly ounded c ys als lacking exsolu ion lamellae. O e all,
hey display sligh ly lowe Al2O3 (0.9-1.4 w %) and C 2O3 (0.3-0.7 w %) con en s compa ed o
po phy oclas s (Fig. 4.6); CaO con en s ange be ween 0.5 and 1.1 w %. Spinel shows C # alues o
52-56 and Mg# alues o 44-47 wi h TiO2 con en s up o 0.1 w %. Fine-g ained (up o 200 µm)
clinopy oxene (diopside) was a ely ound, locally associa ed o neoblas ic oli ine in small
embaymen s on po phy oclas ic o hopy oxene im. I displays (Fig. 4.7) e y high Mg# alues (94-
95) coupled o C 2O3 con en s anging om 0.4 o 0.8 w % and low Al2O3 con en s (1.0-1.5 w %).
Tiny amphibole wi h pseudo-p isma ic o ounded shape may be associa ed wi h he neoblas ic
assemblage. I has an edeni ic composi ion (acco ding o Leake e al., 1997) and Mg# alues o 91-
92, high C 2O3 (2.0-2.6 w %) and low TiO2 con en s (≤0.2 w %).
Up o 0.5 cm- hick eins made o alc ± calci e ± magne i e c osscu he ha zbu gi e olia ion.
Close o he ein, ha zbu gi ic o hopy oxenes may be eplaced by he seconda y mine al ein
assemblage. Fu he away, alc + calci e occasionally occu as small eins cu ing he o hopy oxene
c ys als and subs i u e he neoblas ic agg ega es.
101
4.5.2. O hopy oxeni es
The o hopy oxeni e samples a e composed o ~95 ol% ens a i ic o hopy oxene and accesso y
C -spinel, bu di e o he mino componen s, as well as o he ex u e.
O hopy oxeni e OU5A shows a disequig anula ex u e made o medium- o coa se-g ained (up
o 0.5 cm) o hopy oxenes se in o a ine-g ained g anoblas ic polygonal ma ix (Fig. 4.4a).
O hopy oxenes ha e a s ubby p isma ic shape and bea e y hin Ca- ich exsolu ion lamellae. They
ha e i egula ims and embaymen s o med by he g anoblas ic polygonal assemblage (Fig. 4.4b).
Locally, some c ys als a e unca ed by he ine-g ained assemblage. The la e is mainly composed
o subhed al o hopy oxene g ains, ~5 ol% clinopy oxene, equen ly showing iple junc ion poin s
(Fig. 4.4c) and accesso y amphibole. G anoblas ic py oxenes do no exhibi exsolu ion lamellae. The
o hopy oxene g ains ha e high Mg# alues (90-91; Fig. 4.6). Al2O3, C 2O3 and CaO con en s sligh ly
diminish om co e (1.8-2.1, 0.7-1.0 and 0.5-1.0 w %, espec i ely) o im (1.6-1.9, 0.5-1.0 and 0.4-
0.6 w %). Clinopy oxene is a diopside up o 100 µm in size. I is cha ac e ised by high Mg# alues
(93), low Al2O3 con en s (2.2-2.5 w %), Na2O and C 2O3 con en s o 0.4-0.5 and 1.0-1.5 w %,
espec i ely (Fig. 4.7). Accesso y amphibole occu s as up o 100 µm in size c ys als in he
g anoblas ic assemblage, subs i u ing clinopy oxene g ains. I is a C - ich (C 2O3 = 1.9-2.3 w %)
edeni e showing nea ly cons an TiO2 and Na2O con en s (~0.4 and ~1.9 w %, espec i ely) and
ema kably high Mg# alues (92-93). Fine-g ained (up o ~250 µm) da k b own o black ch omian
(C # = 57-61; Fig. 4.8) spinel occu s h oughou he sample. I has cubic o anhed al habi us and
ela i ely low TiO2 con en s (~0.1 w %) coupled o Mg# alues o 45-48. The sample is c osscu by
up o ~1.5 mm-sized eins o seconda y alc + calci e ± magne i e.
Sample OU8 is an oli ine-bea ing o hopy oxeni e (Ol ~5 ol%), showing a medium- o coa se-
g ained cumuli ic ex u e. O hopy oxene mainly has a s ubby shape (Fig. 4.4d) and is up o 1.5 cm
in size. I is equen ly highly ac u ed, bu clea ages a e s ill well iden i iable. O hopy oxene (Fig.
4.6) has high Mg# alues (92), Al2O3, C 2O3 and CaO con en s compa able o hose o he sample
OU5a (1.5-1.9, 0.5-0.8 and 0.4-0.9 w %, espec i ely). Oli ine (Fig. 4.9; Fo = 92 mol%; NiO = 0.5-
0.6 w %) shows ounded o anhed al habi us and is up o 1.5 mm. Locally, i is included a he
o hopy oxene im (Fig. 4.4e). Spinel is a da k b own o black c ys al up o 500 µm in size, displaying
cubic, p isma ic o anhed al shapes. I s TiO2 con en s each up o 0.1 w %. Mg# alues ange om
56 o 64 and C # alues clus e a ~52 Veins consis ing o alc + calci e cu he o hopy oxeni e.
Locally, anhed al, elonga ed spinel is associa ed o he seconda y assemblage.
4.5.3. Amphibole-bea ing webs e i es

102
Ens a i ic o hopy oxene (~ 25-70 ol%) and augi ic o diopsidic clinopy oxene (~ 25 ol%) a e
he main cons i uen s o he sampled webs e i es. Edeni ic amphibole occu s in a iable amoun s (~
5-40 ol%) and plagioclase is locally p esen (up o ~ 3 ol% in sample OU1). Spinel occu s as an
accesso y phase. In samples OU1 and OU4, he ex u e is disequig anula and is made o medium- o
coa se-g ained (up o ~ 2.5 mm) py oxenes se in o a ine- o medium-g ained g anoblas ic polygonal
assemblage (Fig. 4.5a).
Medium- o coa se-g ained py oxenes ha e p isma ic o subhed al habi us and oc agonal basal
sec ions a e locally obse ed. They locally show mu ual hin exsolu ion lamellae and a e
cha ac e ised by nume ous inclusions. The la e a e mos ly concen a ed a he co e egion and
mainly consis o ounded, abula , o anhed al amphibole. O hopy oxene and spinel (TiO2 = 0.6
w %, C # = 0.7 and Mg# = 22) a e mino inclusions. Clinopy oxene wins can also be easily ound
(Fig. 4.5b).
The g anoblas ic polygonal ma ix (down o ~ 100 µm) is cons i u ed by o hopy oxene ±
clinopy oxene ± amphibole ± plagioclase (Fig. 4.5c) and equen ly shows iple junc ion poin s.
In e loba e, i egula bounda ies among c ys als a e locally obse ed. Rec ys allized py oxenes lack
exsolu ion lamellae and a e some imes subs i u ed by amphibole a hei ims. Amphibole is g een o
ligh b own c ys al showing a pseudo-p isma ic o anhed al habi us. I mainly occu s as an in e s i ial
phase and locally displays a poikili ic ex u e su ounding py oxenes (Fig. 4.5d). Cubic spinel g ains
a e a ely included (TiO2 = 2.3 w %, C # = 66-73 and Mg# ~ 8).
A webs e i e sample (OU7B) consis s o coa se-g ained (up o ~ 2 cm) subhed al clinopy oxene,
o hopy oxene and amphibole displaying mu ually in e inge ed c ys als. They mos ly sha e
in e loba e bounda ies and mu ual inclusions (Fig. 4.5e). Up o 1 mm amphibole and apa i e g ains
a e ound associa ed o medium-g ained py oxenes collec i ely in e sec ing a cm-sized amphibole
c ys al. Apa i e has a p isma ic o ounded shape and is associa ed o amphibole (Fig. 4.5 ). Ra e Fe-
Ni sulphides occu as cubic c ys als in amphibole. Edeni ic amphibole and py oxenes a e commonly
subs i u ed by seconda y emoli e (Al2O3 = 1.3-3.6 w %, Mg# = 92-95), no ably owa ds he con ac
wi h he hos ha zbu gi e.
Locally, ma ic mine als may be pa ially al e ed in o a mix u e o chlo i e + se pen ine + alc ±
smec i e. Webs e i e OU1 shows in e s i ial pa ches made o se ici e.
Mine al majo elemen composi ions a e o e all homogeneous among he samples and ex u e-
ela ed chemical a ia ions we e no obse ed. O hopy oxene has ela i ely low Al2O3 con en s (0.6-
1.2 w %; Fig. 4.6). CaO con en s ange om 0.6 o 0.9 w %. C 2O3 con en s (0.1-0.4 w %) inc ease
a dec easing Mg# alues (78-89). Clinopy oxene shows ela i ely low Al2O3, C 2O3 (Fig. 4.7) and
Na2O con en s (0.6-2.1, 0.1-0.3 and 0.1-0.4 w %, espec i ely). Highe TiO2 con en s (0.1-0.2 w %)
103
a e coupled o p og essi ely lowe Mg# alues (81-90). Edeni e la gely displays inc easing TiO2
con en s (0.3-1.2 w %) wi h inc easing Al2O3 con en s (7.5-11 w %). Mg# alues ange om 78 o
88, whils Na2O con en s mainly clus e a ~1.5-2.0 w %. Plagioclase has 82-86 mol% ano hi e.
Fig. 4.3. Thin sec ion pho omic og aphs unde c oss-pola ized ligh o Ouassé ha zbu gi es. (a)
Po phy oclas ic ex u e. (b) Myloni ic ex u e wi h coa se-g ained o hopy oxene po phy oclas
associa ed wi h he neoblas ic assemblage. (c) Highly s e ched o hopy oxene po phy oclas , showing
aspec a io o 12:1. (d) T ails o spinel g ains. Mine al abb e ia ions a e a e Whi ney and E ans
(2010).
Ol
Opx
Opx
Ol
Spl
104
Fig. 4.4. Thin sec ion pho omic og aphs unde c oss-pola ized (a,b,d,e) and plane-pola ized (c) ligh o
Ouassé o hopy oxeni es. (a,b) Medium- and coa se-g ained o hopy oxenes se in o a ine-g ained
g anoblas ic polygonal ma ix in o hopy oxeni e OU5A. (c) G anoblas ic polygonal c ys als showing
iple junc ion poin s in o hopy oxeni e OU5A. (d) Coa se-g ained o hopy oxene in o hopy oxeni e
OU8. (e) Oli ine c ys al included a he o hopy oxene im in o hopy oxeni e OU8. Mine al
abb e ia ions a e a e Whi ney and E ans (2010).
Opx
Cpx
Opx
Cpx
Opx
Opx
Cpx
Opx
Spl
Opx
Ol
105
Fig. 4.5. Thin sec ion pho omic og aphs unde c oss-pola ized (a,b,e, ) and plane-pola ized (c,d) ligh o
Ouassé amphibole-bea ing webs e i es. (a) Medium- o coa se-g ained py oxenes se in o a g anoblas ic
polygonal assemblage in webs e i e OU4. (b) Clinopy oxene winned c ys al in webs e i e OU1. (c)
Amphibole c ys al associa ed wi h he g anoblas ic polygonal assemblage in webs e i e OU1. (d) Poikili ic
amphibole su ounding py oxenes in webs e i e OU1. (e) Tex u e o webs e i e OU7B. ( ) Apa i e c ys al
associa ed wi h amphibole in webs e i e OU7B. Mine al abb e ia ions a e a e Whi ney and E ans (2010).
Opx
Cpx
Cpx
Amp
Pl
Cpx
Opx
Amp
Amp
Ap
Amp
Cpx
Opx
Ap
112
Fig. 4.12. Ra e Ea h Elemen s composi ions o Ouassé py oxeni es no malized o chond i e
(no malizing alues a e Sun and McDonough, 1989). Field o New Caledonia ha zbu gi es
includes da a om Ma chesi e al. (2009), Ul ich e al. (2010), Secchia i e al. (2020).
Fig. 4.13. Ex ended incompa ible ace elemen diag am o Ouassé py oxeni es
no malized o P imi i e Man le (no malizing alues a e Sun and McDonough, 1989).
Field o New Caledonia ha zbu gi es includes da a om Ma chesi e al. (2009), Ul ich
e al. (2010), Secchia i e al. (2020).

113
4.7.2. Amphibole-bea ing webs e i es
Clinopy oxene has REE con en s anging om ~2 o 10 imes chond i ic alues. I shows a iably
deple ed LREE (LaN/SmN = 0.1-0.6), weak o mode a e nega i e Eu anomalies (Eu/Eu* = 0.7-0.9)
and nea ly la HREE. In addi ion, nega i e anomalies a e obse ed o Pb, S , Z and Ti elemen s
(Fig. 4.14).
O hopy oxene has e y low REE con en s in OU1 and OU4 webs e i es (~ 0.1-1 imes chond i ic
alues), whils highe concen a ions a e displayed by sample OU7B (~1-4 imes chond i ic alues).
The o hopy oxene is cha ac e ized by inc easing concen a ions om LREE o HREE.
O hopy oxene om sample OU7B has a posi i e Eu anomaly (Eu/Eu* = 1.8).
Amphibole displays high REE con en s, up o 30 imes chond i ic alues. I has a con ex REE
pa e n cha ac e ized by a s ong deple ion in LREE (LaN/SmN = 0.2-0.7) and HREE (GdN/YbN = 1.9-
2.0) and a e y weak nega i e Eu anomaly (Eu/Eu* = 0.9). Amphibole om sample OU7B displays
a posi i e LREE ac iona ion o e HREE, Fig. 4.15). In P imi i e Man le no malized ace elemen
diag am all amphiboles show nega i e peaks in Pb, S and Z . The edeni ic amphibole om he
ec ys allized ma ix o ha zbu gi e sample OU7A shows REE con en s up o ~10 imes chond i ic
alues, cha ac e ized by a s ong LREE en ichmen (LaN/SmN = 1.6) and MREE posi i ely
ac iona ed o e HREE (GdN/YbN = 1.3). I b oadly mi o s he amphibole REE pa e n o he hos
webs e i e OU7B, bu a lowe absolu e concen a ions.
Plagioclase om py oxeni e OU1 has high LREE concen a ions (mos ly ~1-5 imes chond i ic
alues; Fig. 4.16), whils M- and HREE con en s a e <1 imes chond i ic alues. I is cha ac e ized
by LREE en ichmen (LaN/SmN = 1.2-4.4) and p ominen posi i e Eu anomalies (Eu/Eu* = 3.3-11).
Apa i e om webs e i e OU7B has ex emely high REE con en s (~20 o ~1100 imes chond i ic
alues; Fig. 4.16), p og essi ely dec easing om LREE o HREE. I shows a s eep L- o MREE
ac iona ion and nea ly la HREE.
114
Fig. 4.14. (a) Ra e Ea h Elemen s and (b) ex ended incompa ible ace elemen s diag ams o
clinopy oxenes om Ouassé py oxeni es no malized o chond i e and P imi i e Man le,
espec i ely (no malizing alues a e Sun and McDonough, 1989). Da a om o he Ouassé
webs e i es s udied by Xu e al. (2021) a e shown o compa ison.
b)
a)
115
Fig. 4.15. (a) Ra e Ea h Elemen s and (b) ex ended incompa ible ace elemen s diag ams
o amphiboles om Ouassé py oxeni es no malized o chond i e and P imi i e Man le,
espec i ely (no malizing alues a e Sun and McDonough, 1989).
b)
a)
116
Fig. 4.16. Ra e Ea h Elemen s composi ions o plagioclase and apa i e om Ouassé amphibole-
bea ing webs e i es OU1 and OU7B, espec i ely. Chond i ic no malizing alues a e a e Sun
and McDonough (1989).
Pl
Ap
117
4.8. Geo he mome y
Equilib ium empe a u es calcula ed o hos ha zbu gi es and enclosed py oxeni e laye s a e
lis ed in Table 4.4. P essu e condi ions we e assumed equal o 1 GPa, conside ing he spinel- acies
condi ions o he hos ha zbu gi es. The applied me hods a e he ollowing:
• wo-py oxene he mome e s o Taylo (1998; e e ed o as TTa98) and B ey and Köhle
(1990; e e ed o as TBK90), based on he Fe2+-Mg exchange be ween coexis ing
clinopy oxene and o hopy oxene
• Ca-in-o hopy oxene he mome e o B ey and Köhle (1990; e e ed o as TCa-in-Opx),
based on he Ca con en o o hopy oxene
• oli ine-spinel he mome e o Jianping e al. (1995; e e ed o as TOl-Spl), based on he
Fe2+-Mg exchange be ween coexis ing oli ine and spinel
• Ca-in-oli ine he mome e o De Hoog e al. (2010; e e ed o as TCa-in-Ol), based on he
Ca con en o oli ine
• amphibole-plagioclase he mome e o Holland and Blundy (1994; e e ed o as THB94),
based on he composi ions o coexis ing amphibole and plagioclase
• he mome e s based on he pa i ioning o slowly di using elemen s (REE-Y), be ween
(i) clinopy oxene and o hopy oxene (Liang e al., 2013; e e ed o as TREE-Px), and (ii)
clinopy oxene and plagioclase (Sun and Liang, 2017; e e ed o as TREE-Cpx-Pl).
The po phy oclas ic assemblage o Ouassé ha zbu gi es yielded Ca-in-Opx empe a u es anging
om 920 o 970 °C a he o hopy oxene co e. Rema kably lowe alues (730-750 °C) we e ob ained
o oli ine-spinel co es. Sligh ly lowe empe a u es we e eco ded by he neoblas ic assemblage (TCa-
in-Opx = 920-945 °C, TTa98 = 880-920 °C, TBK90 = 890-930 °C, TOl-Spl = 720 °C).
O hopy oxeni e OU5A eco ded Ca-in-Opx empe a u es o 920-930 °C, TTa98 = 894 °C and
TBK90 = 910 °C. O hopy oxene co es om sample OU8 eco ded he lowes Ca-in-Opx empe a u es
(870 °C). Oli ine-spinel and Ca-in-oli ine he mome e s ga e alues o 865 and 861 °C, espec i ely,
consis en wi h he Ca-in-Opx es ima e.
The mome e s based on slowly di using elemen s (REE, Y) we e applied on he webs e i ic
assemblages. Sample OU1 yielded alues o 1251 ± 37 °C o he clinopy oxene-o hopy oxene pai
and alues o 1310 ± 14 °C we e p o ided by clinopy oxene and plagioclase. Compa able
empe a u es we e ob ained om he co e o he coa se clinopy oxene-o hopy oxene (1264 ± 50 °C)
and he co e o he g anoblas ic py oxenes (1249 ± 52 °C) om sample OU4. Con en ional
geo he mome y applied o py oxene co es p o ided TCa-in-Opx = 965-995 °C, TTa98 = 930-970 °C and

118
TBK90 = 915-965 °C. These alues a e in he ange o hose om he hos ha zbu gi es. The amphibole-
plagioclase geo he mome e applied on sample OU1 ga e consis en empe a u es o 970 °C.
4.9. 40A /39A amphibole da ing
Two magma ic amphibole (edeni e) sepa a es om webs e i es OU1 and OU7B we e analysed
o 40A /39A da ing and he esul s a e epo ed in Table 4.5 and Figu e 4.17.
The wo samples show low amoun s o excess a gon (40A /36A = ~295-297) and display good
conco dances be ween he pla eau ages and he isoch on ages (Tab. 4.5). Well-de ined pla eau ages
can be seen in Figu e 4.17.
The pla eau ages o he wo samples (OU1 = 56.01 ± 0.19 Ma; OU7B = 56.05 ± 0.17 Ma) a e
nea ly undis inguishable and clus e a 56 Ma.
4.10. Discussion
4.10.1. Na u e and e olu ion o hos ing pe ido i es
O e all, majo elemen mine al and whole ock composi ions o he Ouassé ha zbu gi es a e in
he ange o he o he New Caledonia man le ha zbu gi es which we e ex ensi ely s udied in p e ious
wo ks (Ma chesi e al., 2009; Ul ich e al., 2010; Secchia i e al., 2020). In pa icula , acco ding o
Secchia i e al. (2020), he ha zbu gi es a e ul a- e ac o y pe ido i es eco ding a wo-s age mel ing
p ocess including an anhyd ous mel ing e en which possibly occu ed in a ma ginal basin and a
subsequen luid-assis ed mel ing in a o ea c en i onmen . Pos -mel ing eac i e pe cola ion o
deple ed mel s led o c ys alliza ion o seconda y py oxenes (e.g., Secchia i e al., 2020) and p oduced
a iable en ichmen s in se e al incompa ible ace elemen s (L- and MREE, LILE and some HFSE,
see also Xu e al., 2021a).
The highly e ac o y na u e o Ouassé ha zbu gi es is suppo ed by (i) he absence o p ima y
clinopy oxene, (ii) he e y low bulk ock Al2O3 (0.4-0.5 w %) and CaO (0.4-0.5 w %) con en s
coupled o high MgO con en s (46-47 w %), (iii) he high C # alues (55-65) coupled o low TiO2
con en s (≤0.1 w %) in spinels, (i ) he high o s e i e con en in oli ine (Fo = 91-92 mol%) and ( )
he high Mg# alues (91-92) o o hopy oxene po phy oclas s associa ed wi h low Al2O3 con en s
(1.1-1.9 w %).
119
OU1 Ho nblende
Fig. 4.17. 40A /39A age spec a o wo amphibole sepa a es om Ouassé webs e i es
OU1 and OU7B.
Fig. 4.18. Z /Nb s. Ti/Nb o amphiboles om Ouassé samples. Fields o sup a-
subduc ion and in apla e amphibole a e a e Col o i e al. (2007).
120
Rema kably, he Ouassé ha zbu gi es we e a ec ed by in ense de o ma ion, ha p oduced
myloni ic ex u es and highly s e ched o hopy oxene po phy oclas s (Fig. 4.3c). De o ma ion in he
s udy a ea is linked o he Bogo a Peninsula Shea Zone, one o he h ee egional-scale high
empe a u e shea zones o he Pe ido i e Nappe (see §Geological and pe ological se ing).
De o ma ion was accompanied by ec ys alliza ion and g ain size educ ion, as es i ied by he ine-
g ained (~ 100-400 µm) neoblas ic assemblage (ol + opx ± spl). Seconda y clinopy oxene c ys allized
among neoblas s, sugges ing de o ma ion synch onous o pe cola ion o mel o luids capable o
p ecipi a e clinopy oxene. Amphibole o edeni ic composi ion was also locally ound wi hin he
neoblas ic assemblage. The p esence o amphibole ela i ely en iched in incompa ible elemen s
(Table 4.3, Fig. 4.15) in a highly deple ed ha zbu gi e poin s o a me asoma ic o igin. I s Ti/Nb and
Z /Nb a ios (Fig. 4.18) a e cohe en wi h an o igin in a sup a-subduc ion zone (Col o i e al., 2007).
Teyssie e al. (2016) also epo ed he p esence o ine-g ained in e s i ial pa gasi e in Bogo a
myloni es. They p oposed ha he high empe a u e amphibole o igina ed om pe cola ing luids
ini ially de i ed om he subduc ion con ex and subsequen ly ela ed o ocean wa e in il a ion.
Ca-in-o hopy oxene equilib a ion empe a u es o neoblas ic py oxenes ange om 920 o 945
°C. These es ima es sugges ai ly high empe a u e condi ions o he de o ma ion. They a e
compa able o hose calcula ed o he po phy oclas ic o hopy oxene (TCa-in-Opx = 890-970 °C), in
ag eemen wi h he absence o signi ican di e ences in majo elemen composi ions be ween
po phy oclas s and neoblas s. These empe a u es all in he ange o hose epo ed by o he au ho s
(Teyssie e al., 2016; Cha za as e al., 2020) o he Bogo a Peninsula Shea Zone. Signi ican ly
lowe empe a u es we e ob ained o neoblas ic (720 °C) and po phy oclas ic (730-750 °C) oli ine-
spinel pai s (Jianping e al., 1995). Conside ing ha he oli ine-spinel he mome e is based on as e
elemen di usion compa ed o he Ca-in-o hopy oxene, he ema kable empe a u e di e ence
de ec ed by he wo geo he mome e s sugges a ela i ely slow cooling and slow he mal equilib a ion
o he s udied man le sec o .
4.10.2. O igin o he py oxeni e laye s
Whole ocks and mine als chemis y o Ouassé o hopy oxeni es and amphibole-bea ing
webs e i es a e consis en wi h he composi ions o sup a-subduc ion zone py oxeni es epo ed in he
li e a u e (see Figs. 4.6,4.7,4.8,4.9,4.10,4.11).
4.10.2.1. O hopy oxeni es
The p esence o o hopy oxeni e laye s in man le sui es is gene ally asc ibed o pe cola ing silica-
ich mel s. Py oxenes om Ouassé o hopy oxeni es a e cha ac e ized by e y low Al2O3 con en s
121
(1.5-2.5 w %) coupled o e y high Mg# alues (90-93), sugges ing an o igin om a sup a-subduc ion
agen , as epo ed, o ins ance, by Mün ene e al. (2001), Mo ishi a e al. (2003) and A ai e al.
(2006) o ocks c ys allized om hyd ous silica- ich mel s showing high Mg# andesi e o bonini e-
a ini y.
The p esence o clinopy oxene in o hopy oxeni e OU5A allowed he calcula ion o pa en al
liquids in equilib ium wi h his mine al. T ace elemen analysis pe o med on clinopy oxene and
cpx/liquid pa i ion coe icien s om he compila ion o Ha and Dunn (1993) e u ned he
composi ion o he equilib ium mel (Tab. 4.6). I s REE pa e n (Fig. 4.19a) shows con en s up o ~
20 imes chond i e alues, wi h LREE posi i ely ac iona ed o e MREE (LaN/SmN = 3.2) and nea ly
la HREE (GdN/YbN = 0.9). Posi i e Ba, Pb and S anomalies and nega i e Ti anomaly a e displayed
in a N-MORB no malized ex ended ace elemen diag am (Fig. 4.19b). En ichmen s in LREE, LILE
(Ba, S ) and Pb a e ypical o slab-de i ed hyd ous silica e mel s, a he han aqueous luids (Zheng,
2019). Mg# o he equilib ium mel (compu ed acco ding o he equa ion o Wood and Blundy, 1997)
is equal o 80. The high Mg# sugges an o igin om a e ac o y sou ce (e.g., Pea ce, 1982).
Acco ding o his, bo h py oxenes ha e e ac o y composi ions wi h high Mg# alues (90-93).
Bonini e-like liquids could be a good candida e o a silica- ich mel in equilib ium wi h such a
deple ed sou ce (Pea ce and Reagan, 2019), as he New Caledonia Pe ido i e Nappe is c osscu by
dikes wi h bonini e a ini y (Cluzel e al., 2006; Xu e al., 2021a) and bonini e ocks we e emplaced
a i s base (Cluzel e al., 2016). Fig. 4.19 shows a good ma ch be ween he calcula ed liquid
ep esen ing he pa en al mel o o hopy oxeni e OU5A and he ield o New Caledonia bonini es,
as well as he pa e n o p e-obduc ion bonini e-like dikes. Bonini ic ocks om New Caledonia we e
in e p e ed as he p oduc o low deg ee pa ial mel ing o a deple ed pe ido i e sou ce p e iously
en iched by slab-de i ed elsic mel s (Cluzel e al., 2016). The small pe cen age o clinopy oxene (~
5 ol%) in sample OU5A likely e lec s he Ca-poo composi ion o he whole ock which could be
explained by he low-Ca na u e o New Caledonia bonini es (Cluzel e al., 2016). Tex u al e idence
show ha he amphibole g ew a he expense o clinopy oxene. I s geochemical ea u es (e.g. Ti/Nb
and Z /Nb a ios Fig. 4.18) a e consis en wi h c ys alliza ion om a subduc ion- ela ed agen
(Col o i e al., 2007). The bonini e-like mel was injec ed in he de o ming ha zbu gi e, as e idenced
by he o ien a ion o he o hopy oxeni e dike conco dan o he pe ido i e olia ion. In addi ion,
equilib a ion empe a u es ga e alues consis en wi h hose o he hos ha zbu gi e (TCa-in-Opx = 920-
930 °C).
The o hopy oxeni e OU8 has peculia ea u es, as (i) he high Ni con en s (2890 ppm), which
exceeds he alues displayed by all he New Caledonia ha zbu gi es and (ii) he ex emely low REE
con en s (< 0.1 imes chond i ic alues). Mos o he elemen s appea ing in he bulk ock ex ended
128
hese ocks and u he ield su eys could enhance he s udies in emo e a eas. Uppe a c c us is
missing (e.g., Cluzel e al., 2012b), hus ende ing di icul o de e mine he exis ence o a FAB c us .
4.10.5. Hin s o ein e p e ing he signi icance o he Bogo a Peninsula Shea Zone
The Bogo a Peninsula Shea Zone (BPSZ) was gene ally conside ed as an oceanic paleo ans o m
aul cha ac e ized by a dex al sense o mo ion (P inzho e and Nicolas, 1980; Ti us e al., 2011;
Cha za as e al., 2020). The new da a on Ouassé man le ocks could p o ide new cons ain s on he
BPSZ o igin.
Ouassé myloni ic ha zbu gi es de eloped seconda y clinopy oxene and amphibole in he
neoblas ic assemblage, sugges ing myloni iza ion concu en o in il a ion o slab-de i ed
luids/mel s. In his iew, he BPSZ was es ablished in a sup a-subduc ion en i onmen . Acco dingly,
he subduc ion- ela ed mel o ming o hopy oxeni e OU5A was injec ed in he ha zbu gi es du ing
de o ma ion, as he py oxeni e laye is conco dan wi h he hos pe ido i es olia ion. As discussed in
he p e ious sec ion, he subsequen in usion o amphibole-bea ing webs e i es is connec ed o a
b i le beha iou o he man le.
Di e en subduc ion- ela ed scena ios could be in oked o explain he o igin o he Bogo a
Peninsula Shea Zone:
• I could ep esen a ans o m aul ela ed o a sho -li ed sp eading cen e de eloped in
he o ea c egion sho ly a e subduc ion ini ia ion. A simila mechanism o sea loo
sp eading was hypo hesised by Reagan e al. (2019) o he Izu-Bonin-Ma iana sys em
• New Caledonia Paleocene-Eocene subduc ion incep ion is hough o occu nea a
sp eading idge and oblique subduc ion has been en isaged (Cluzel e al., 2021). The
esul ing ansp essi e o ces could ha e de o med he ho and buoyan li hosphe ic
man le, hus c ea ing he BPSZ
• The BPSZ could ep esen an old (La e C e aceous-Paleocene) ans o m aul o a leas
a weak li hosphe ic man le egion o he Sou h Loyal y Basin eac i a ed du ing he
beginning o he Paleocene-Eocene subduc ion
Some conside a ions can be made in o de o gi e a leas some p e e ences o e he abo e
op ions. Fi s , myloni iza ion occu ed a e pa ial mel ing o pe ido i es, no p io as pa ial mel ing
could in luence o hide de o ma ion ex u es. Since Ouassé pe ido i es, like he o he New Caledonia
ha zbu gi es, a e in e p e ed o eco d subduc ion- ela ed luid-assis ed pa ial mel ing, de o ma ion
is p esumed o ha e occu ed a e his e en and hus he hi d op ion can be disca ded, as i would
include a p e-exis ing shea zone p eceding he subduc ion- ela ed pa ial mel ing e en . The i s wo

129
op ions seem o be mo e plausible and addi ional da a a e needed o be e in e p e he o igin o he
BPSZ.
4.11. Conclusions
The Ouassé man le sec ion shows a a e a ie y o subduc ion- ela ed py oxeni es c osscu ing
he hos ha zbu gi es. In pa icula , o hopy oxeni es and amphibole-bea ing webs e i es we e
ecognized. Each s udied sample displays peculia mine alogical cha ac e is ics, whe eby, o
ins ance, Ol-bea ing and Cpx-bea ing o hopy oxeni es we e dis inguished. In addi ion, he
webs e i ic ocks ha e a iable amoun s o p ima y amphibole (~5-40 ol%). F om a chemical poin
o iew, he o hopy oxeni es show mo e e ac o y composi ions compa ed o he amphibole-bea ing
webs e i es.
Beyond he cha ac e iza ion o he py oxeni ic samples, he main achie emen s o his PhD Thesis
we e (i) he iden i ica ion o hei pa en al liquids and (ii) hei signi icance in he o e iew o he
Eocene subduc ion. The main conclusions a e:
• Equilib ium mel s o he o hopy oxeni es ha e a bonini e-a ini y.
• Equilib ium mel s o he amphibole-bea ing webs e i es a e mo e en iched
liquids compa ed o hose o he o hopy oxeni es. A de i a ion om en iched
bonini ic liquids and/o om adaki e-like liquids is plausible.
• The 40A /39A cooling age o ~56 Ma e e ed o he webs e i es sugges ha
Ouassé py oxeni es ep esen one o he ea lies magma ic p oduc s o mel
pe cola ion in he New Caledonia o ea c man le epo ed in he li e a u e.
The esul s also allowed o gi e new insigh s on he signi icance o he Bogo a Peninsula Shea
Zone (BPSZ). In pa icula , he conco dan o hopy oxeni e laye ound in he myloni ic ha zbu gi es
indica es he injec ion o bonini ic liquids concu en o he ac i i y o he BPSZ. As he bonini e-like
liquids a e ypically subduc ion- ela ed p oduc s, he shea zone should ha e been de eloped in a
sup a-subduc ion se ing. Thus, i canno be conside ed as a paleo ans o m aul me ely ela ed o a
no mal oceanic sp eading idge, as p oposed by P inzho e and Nicolas (1980), Ti us e al. (2011)
and Cha za as e al. (2020).
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144
Table 4.3. Rep esen a i e ace elemen composi ions (ppm) o mine als om Ouassé py oxeni es.
Sample
OU1
OU4
OU5A
OU7B
OU8
Rock ype
Amp-webs e i e
Amp-webs e i e
O hopy oxeni e
Amp-webs e i e
O hopy oxeni e
Mine al
Opx
Cpx
Amp
Pl
Opx
Cpx
Amp
Opx
Cpx
Amp
Opx
Cpx
Amp
Ap
Opx
Ol
Sc
27
90
115
3.58
23
89
125
20
62
71
6.33
68
73
16
14
1.88
Ti
649
1168
8711
41
442
904
7592
203
465
1781
144
638
6323
872
17
3.80
V
72
357
588
0.88
64
198
587
94
216
398
19
257
461
33
87
1.03
C
1007
706
1846
6.78
1329
1271
4216
5792
7729
11484
41
539
1167
148
4681
38
Co
101
39
65
0.45
92
37
69
68
36
49
70
32
48
6.56
61
164
Ni
433
312
557
1.45
526
290
753
934
646
1197
661
408
779
21
944
4179
Zn
128
30
45
2.73
89
21
40
38
15
18
39
19
33
165
36
42
Rb
0.14
0.08
0.31
bdl
bdl
0.10
0.36
0.12
0.09
0.60
0.20
0.05
0.24
31
0.04
0.04
S
0.18
20
67
690
0.16
25
63
0.46
17
21
0.34
28
56
669
0.11
0.14
Y
0.83
10
20
0.11
0.58
5.58
15
0.36
2.78
5.23
0.77
5.03
15
23
0.05
bdl
Z
0.58
8.64
26
bdl
0.58
7.50
26
0.40
3.21
5.98
0.69
10
63
100
bdl
0.04
Nb
0.06
0.03
1.06
bdl
0.06
0.05
0.50
0.07
0.04
0.21
0.12
0.04
3.31
3.02
0.03
0.03
Cs
0.04
0.01
0.02
0.11
0.01
0.03
0.02
0.02
0.01
bdl
0.06
bdl
0.02
1.10
0.01
0.01
Ba
0.04
0.14
3.55
4.52
0.03
0.27
5.12
0.25
0.22
3.09
0.10
0.11
6.14
220
0.08
0.06
La
0.02
0.39
1.17
0.70
bdl
0.45
1.43
bdl
0.22
0.45
bdl
1.10
4.06
161
0.02
0.01
Ce
bdl
2.47
6.25
1.43
0.07
2.39
6.89
0.06
0.71
1.64
0.08
4.78
18
713
0.01
bdl
P
0.01
0.59
1.39
0.15
bdl
0.49
1.34
bdl
0.11
0.23
0.08
0.82
3.12
47
0.01
bdl
Nd
0.10
4.17
10
0.42
bdl
2.76
8.01
0.07
0.75
1.32
0.39
3.92
15
113
0.10
0.06
Sm
0.05
1.78
3.78
0.20
bdl
1.03
2.51
0.08
0.24
0.34
0.31
1.12
3.59
18
0.02
0.07
Eu
0.04
0.41
1.20
0.29
0.02
0.34
0.95
0.07
0.12
0.17
0.20
0.27
1.07
4.97
0.04
0.02
Gd
0.14
2.01
4.57
0.17
bdl
1.36
3.47
0.17
0.35
0.75
0.37
1.22
3.38
4.45
0.07
0.06
Tb
bdl
0.32
0.66
0.05
0.02
bdl
0.53
0.03
bdl
0.13
0.10
0.17
0.46
1.08
bdl
bdl
Dy
bdl
2.12
4.67
0.54
0.15
1.23
3.06
bdl
0.49
0.91
bdl
1.10
3.01
6.30
0.01
bdl
Ho
0.04
0.43
0.83
bdl
0.03
bdl
0.61
0.04
0.12
0.20
bdl
0.23
0.57
1.11
bdl
0.01
E
0.15
1.08
2.19
0.31
0.12
0.67
1.45
bdl
0.34
0.55
0.34
bdl
1.65
5.36
0.07
0.05
Tm
bdl
0.16
0.31
0.12
bdl
0.10
0.23
0.02
bdl
0.10
0.07
0.09
0.22
bdl
0.01
bdl

145
Yb
0.22
0.94
2.04
bdl
0.12
0.61
1.54
0.16
bdl
0.54
bdl
0.56
1.39
bdl
0.12
0.08
Lu
0.05
0.13
0.24
0.02
0.02
0.09
0.20
0.02
0.04
0.08
0.09
0.08
0.20
1.10
0.01
bdl
H
0.15
0.49
1.32
1.08
0.04
0.42
1.01
0.07
0.18
0.15
0.52
0.32
2.38
3.54
0.29
bdl
Ta
0.01
0.02
0.07
0.02
bdl
0.04
0.07
0.02
0.03
0.01
0.07
0.01
0.19
1.75
bdl
0.02
Pb
0.10
0.05
0.10
0.40
0.02
0.09
0.07
0.04
0.06
bdl
bdl
0.06
0.11
25
0.03
0.03
Th
0.02
0.02
0.03
0.02
bdl
0.04
0.12
0.03
0.01
0.01
0.14
0.04
0.06
6.25
0.02
0.01
U
0.03
0.01
0.04
0.05
bdl
0.03
0.02
0.01
0.02
0.01
bdl
0.03
0.05
6.43
0.01
0.01
bdl = below de ec ion limi s
146
Table 4.4. Tempe a u e es ima es (°C) o Ouassé pe ido i es and py oxeni es. Calcula ions we e
made conside ing he co e analysis o each g ain and p essu e condi ions o 1 GPa.
TREE-Pxa
TREE-Cpx-Plb
TCa-in-Opxc
TTa98d
TBK90c
TAmp-Ple
TOl-Spl
TCa-in-Olg
Ha zbu gi e OU2
po phy oclas
956
747
neoblas
923
883
892
721
Ha zbu gi e OU3
po phy oclas
973
neoblas
945
923
934
721
Ha zbu gi e OU7A
po phy oclas
923
728
Amp-webs e i e OU1
medium- o coa se-g ained py oxenes
1251 ± 37
990
958
923
g anoblas ic assemblage
1310 ± 14
997
992
946
970
Amp-webs e i e OU4
medium- o coa se-g ained py oxenes
1264 ± 50
965
941
927
g anoblas ic assemblage
1249 ± 52
971
927
914
O hopy oxeni e OU5A
medium- o coa se-g ained py oxenes
924
g anoblas ic assemblage
932
894
911
Amp-webs e i e OU7B
993
970
965
O hopy oxeni e OU8
869
865
861
a= Liang e al. (2013)
b= Sun and Liang (2017)
c= B ey and Köhle (1990)
d= Taylo 1998
e= Holland and Blundy (1994)
= Jianping e al. (1995)
g= De Hoog e al. (2010)
147
Table 4.5. Summa y o 40A /39A esul s o ho nblende analysis
Pla eau Age
Isoch on Age
In eg a ed age
Sample
I ad
min
Calcula ion
n
%39A
MSWD
Age(Ma)
±
1s
40A /36A
±
1s
Age(Ma)
±
1s
n
Age(Ma)
±
1s
OU7B
NM-312A
Ho nblende
WMA
10
97.0
0.44
56.05
±
0.17
297.3
±
4.4
55.87
±
0.47
12
56.57
±
0.24
OU1
NM-312A
Ho nblende
WMA
12
100.0
0.50
56.01
±
0.19
295.4
±
0.8
56.03
±
0.22
12
55.98
±
0.30
I adia ion = NM-312A
WMA = Weigh ed mean age
148
Table 4.6. T ace elemen s composi ions and Mg# alues o calcula ed liquids in equilib ium wi h
clinopy oxenes om Ouassé py oxeni es.
Sample
OU1
OU4
OU5A
OU7B
Rock ype
Amp-webs e i e
Amp-webs e i e
O hopy oxeni e
Amp-webs e i e
Ti
3040
2355
1211
1662
V
115
64
70
87
Rb
448
566
491
253
Ba
212
352
565
162
Th
122
176
28
182
U
23
53
33
53
Nb
3.99
6.19
5.45
4.91
La
7.34
8.35
4.11
20
Ce
29
28
8.28
56
Pb
0.80
1.12
0.81
0.88
P
4.22
3.54
0.80
5.88
S
157
194
95
222
Nd
22
15
3.99
21
Sm
6.12
3.55
0.82
3.84
Z
70
61
26
78
H
2.07
1.65
0.71
1.25
Eu
1.17
0.97
0.34
0.76
Gd
5.02
3.39
0.88
3.04
Dy
4.79
2.78
1.11
2.49
Y
21
12
5.96
11
E
2.79
1.74
0.88
1.22
Yb
2.18
1.42
0.74
1.30
Lu
0.29
0.21
0.08
0.20
S /Y
7.38
16
16
21
La/Yb
3.36
5.88
5.53
16
Mg#
58
67
80
69
149
Chap e 5
5.1. Concluding ema ks
The p esen PhD Thesis ocused on man le sequences om he Ex e nal Ligu ian and New
Caledonia ophioli es. The Ex e nal Ligu ian ophioli es expose a li hosphe ic man le o subcon inen al
o igin ha unde wen a decomp ession e olu ion du ing he Mesozoic i ing s age ha p eceded he
opening o he Ju assic Wes e n Te hys basin. The New Caledonia ophioli es expose a li hosphe ic
man le o oceanic na u e ha expe ienced mel ex ac ion in a o ea c en i onmen du ing he La e
Eocene subduc ion phase. Despi e hese di e ences, bo h s udied man le sec ions a e cha ac e ized
by a a ie y o py oxeni e laye s. In addi ion, la ge-scale li hosphe ic shea zones we e de ec ed bo h
in he Ex e nal Ligu ian (Mon e San ’Agos ino) and New Caledonia (Bogo a Peninsula Shea Zone)
ophioli es. The Mon e San ’Agos ino shea zone accommoda ed he de o ma ion o he
subcon inen al man le du ing a i ing- ela ed exhuma ion e en . The Bogo a Peninsula Shea Zone
has been ein e p e ed as a paleo ans o m aul de eloped du ing he subduc ion phase.
Besides he speci ic objec i es o each case s udy, he esul s o he Thesis could be ead in e ms
o he he e ogenei ies exhibi ed by he man le sequences. Lis ed below some obse a ions
(abb e ia ions: EL = Ex e nal Ligu ian case s udy; NC = New Caledonia case s udy):
• EL: Conside ing he s udied man le bodies (Mon e Ga i and Mon e San ’Agos ino) and
he o he s case s udies epo ed in he li e a u e, he Thesis has shown a he e ogeneous
i ing- ela ed plagioclase- acies e olu ion, cha ac e ized by p esence o absence o
myloni ic o ul amyloni ic de o ma ion, and p esence o absence o mel - ock eac ion
e en s.
• EL: The Mon e Ga i man le body documen s he occu ence o a plagioclase- acies mel
imp egna ion e en in he la e T iassic. The mel imp egna ion e en eco ded by he
Mon e Ne o man le body con e sely mos likely de eloped in he middle-la e Ju assic.
These age di e ences highligh he polyphase na u e o he i ing- ela ed man le
e olu ion, which p esumably occu ed in a ime span o ~60 Ma.
• NC: The s udied man le sequence (nea Ouassé, Bogo a Peninsula) o e s an ex eme
py oxeni e he e ogenei y wi hin ew hund ed me e s. These py oxeni es p o ide e idence
o : (i) he p esence o composi ionally di e se subduc ion- ela ed magmas, and (ii) a
a iable geochemical con ibu ion o he sinking slab in he o ea c man le.